According to Lechtman, Europeans sought to optimize metals' "hardness, strength, toughness, and sharpness." The Inka, by contrast, valued "plasticity, malleability, and toughness." Europeans used metal for tools. Andean societies primarily used it as a token of wealth, power, and community affiliation. European metalworkers tended to create metal objects by pouring molten alloys into shaped molds. Such foundries were not unknown to the Inka, but Andean societies vastly preferred to hammer metal into thin sheets, form the sheets around molds, and solder the results. The results were remarkable by any standard-one delicate bust that Lechtman analyzed was less than an inch tall but made of twenty-two separate gold plates painstakingly joined.

If a piece of jewelry or a building ornament was to proclaim its owner's status, as the Inka desired, it needed to shine. Luminous gold and silver were thus preferable to dull iron. Because pure gold and silver are too soft to hold their shape, Andean metalworkers mixed them with other metals, usually copper. This strengthened the metal but turned it an ugly pinkish-copper color. To create a lustrous gold surface, Inka smiths heated the copper-gold alloy, which increases the rate at which the copper atoms on the surface combine with oxygen atoms in the air-it makes the metal corrode faster. Then they pounded the hot metal with mallets, making the corrosion flake off the outside. By repeating this process many times, they removed the copper atoms from the surface of the metal, creating a veneer of almost pure gold. Ultimately the Inka ended up with strong sheets of metal that glittered in the sun.

Andean cultures did make tools, of course. But rather than making them out of steel, they preferred fiber. The choice is less odd than it may seem. Mechanical engineering depends on two main forces: compression and tension. Both are employed in European technology, but the former is more common-the arch is a classic example of compression. By contrast, tension was the Inka way. "Textiles are held together by tension," William Conklin, a research associate at the Textile Museum in Washington, D.C., told me. "And they exploited that tension with amazing inventiveness and precision."

In the technosphere of the Andes, Lechtman explained, "people solved basic engineering problems through the manipulation of fibers," not by creating and joining hard wooden or metal objects. To make boats, Andean cultures wove together reeds rather than cutting up trees into planks and nailing them together. Although smaller than big European ships, these vessels were not puddle-muddlers; Europeans first encountered Tawantinsuyu in the form of an Inka ship sailing near the equator, three hundred miles from its home port, under a load of fine cotton sails. It had a crew of twenty and was easily the size of a Spanish caravelle. Famously, the Inka used foot-thick cables to make suspension bridges across mountain gorges. Because Europe had no bridges without supports below, they initially terrified Pizarro's men. Later one conquistador reassured his countrymen that they could walk across these Inka inventions "without endangering themselves."

Andean textiles were woven with great precision-elite garments could have a thread count of five hundred per inch-and structured in elaborate layers. Soldiers wore armor made from sculpted, quilted cloth that was almost as effective at shielding the body as European armor and much lighter. After trying it, the conquistadors ditched their steel breastplates and helmets wholesale and dressed like Inka infantry when they fought.

Although Andean troops carried bows, javelins, maces, and clubs, their most fearsome weapon, the sling, was made of cloth. A sling is a woven pouch attached to two strings. The slinger puts a stone or slug in the pouch, picks up the strings by the free ends, spins them around a few times, and releases one of the strings at the proper moment. Expert users could hurl a stone, the Spanish adventurer Alonso Enriquez de Guzman wrote, "with such force that it will kill a horse.... I have seen a stone, thus hurled from a sling, break a swordin two pieces when it was held in a man's hand at a distance of thirty paces." (Experimenting with a five-foot-long, Andean-style sling and an egg-sized rock from my garden, I was able, according to my rough calculation, to throw the stone at more than one hundred miles per hour. My aim was terrible, though.) In a frightening innovation, the Inka heated stones in campfires until they were red hot, wrapped them in pitch-soaked cotton, and hurled them at their targets. The cotton caught fire in midair. In a sudden onslaught the sky would rain burning missiles. During a counterattack in May 1536 an Inka army used these missiles to burn Spanish-occupied Qosqo to the ground. Unable to step outside, the conquistadors cowered in shelters beneath a relentless, weeks-long barrage of flaming stone. Rather than evacuate, the Spanish, as brave as they were greedy, fought to the end. In a desperate, last-ditch counterattack, the Europeans eked out victory.

More critical than steel to Pizarro's success was the horse. The biggest animal in the Andes during Inka times was the llama, which typically weighs three hundred pounds. Horses, four times as massive, were profoundly, terribly novel. Add to this the shock of observing humans somehow astride their backs like half-bestial nightmare figures and it is possible to imagine the dismay provoked by Pizarro's cavalry. Not only did Inka infantrymen have to overcome their initial stupefaction, their leaders had to reinvent their military tactics while in the midst of an invasion. Mounted troops were able to move at rates never encountered in Tawantinsuyu. "Even when the Indians had posted pickets," Hemming observed, "the Spanish cavalry could ride past them faster than the sentries could run back to warn of danger." In clash after clash, "the dreaded horses proved invincible." But horses are not inherently unbeatable; the Inka simply did not discover quickly enough where they had an advantage: on their roads.

The conquistadors disparaged steep Inka highways because they had been designed for sure-footed llamas rather than horses. But they were beautifully made-this road, photographed in the 1990 s, had lasted more than five hundred years without maintenance.

European-style roads, constructed with horses and cars in mind, view flatness as a virtue; to go up a steep hill, they use switchbacks to make the route as horizontal as possible. Inka roads, by contrast, were built for llamas. Llamas prefer the coolness of high altitudes and, unlike horses, readily go up and down steps. As a result, Inka roads eschewed valley bottoms and used long stone stairways to climb up steep hills directly-brutal on horses' hooves, as the conquistadors often complained. Traversing the foothills to Cajamarca, Francisco Pizarro's younger brother Hernando lamented that the route, a perfectly good Inka highway, was "so bad" that the Spanish "could not use horses on the roads, not even with skill." Instead the conquistadors had to dismount and lead their reluctant animals through the steps. At that point they were vulnerable. Late in the day, Inka soldiers learned to wait above and roll boulders on their foes, killing some of the animals and frightening others into running away. Men left behind could be picked off at leisure. Multiple ambushes cost the lives of many Spanish troops and animals.

To be sure, horses confer an advantage on flat ground. But even on the plains the Inka could have won. Foot soldiers have often drubbed mounted troops. At the battle of Marathon in 490 B.C., the outnumbered, outarmored Athenian infantry destroyed the cavalry of the Persian emperor Darius I. More than six thousand Persians died; the Greeks lost fewer than two hundred men. So dire had the situation initially appeared that before the fight Athens sent a messenger to Sparta, its hated rival, to beg for aid. In the original marathon, the courier ran more than a hundred miles in two days to deliver his message. But by the time the Spartan reinforcements arrived, there was nothing to see but dead Persians.

The Inka losses were not foreordained. Their military was hampered by the cult of personality around its deified generals, which meant both that leaders were not easily replaced when they were killed or captured and that innovation in the lower ranks was not encouraged. And the army never learned to bunch its troops into tight formations, as the Greeks did at Marathon, forming human masses that can literally stand up to cavalry. Nonetheless, by the time of the siege of Qosqo the Inka had developed an effective anti-cavalry tactic: bolas. The Inka bola consisted of three stones tied to lengths of llama tendon. Soldiers threw them, stones a-whirl, at charging horses. The weapons wrapped themselves around the animals' legs and brought them down to be killed by volleys of sling missiles. Had the bolas come in massed, coordinated onslaughts instead of being wielded by individual soldiers as they thought opportune, Pizarro might well have met his match.

If not technology or the horse, what defeated the Inka? As I said, some of the blame should be heaped on the overly centralized Inka command structure, a problem that has plagued armies throughout time. But another, much larger part of the answer was first stated firmly by Henry Dobyns. During his extracurricular reading about Peru, he came across a passage by Pedro Cieza de Leon, the Spanish traveler who observed three roads between the same two cities. Entranced by the first exhibition of Inka booty in Spain, Cieza de Leon had crossed the Atlantic as a teenager and spent fifteen years in Peru, Bolivia, Ecuador, and Colombia, traveling, fighting, and taking notes for what would become a massive, three-volume survey of the region. Only the first part was printed in his lifetime, but by the twentieth century historians had found and published most of the rest. Dobyns learned something from Cieza de Leon that was not mentioned in Prescott's history, in the Smithsonian's official Handbook of South American Indians, or in any of the then-standard descriptions of Tawantinsuyu. According to Cieza de Leon, Wayna Qhapaq, Atawallpa's father, died when "a great plague of smallpox broke out [in 1524 or 1525], so severe that more than 200,000 died of it, for it spread to all parts of the kingdom."

Smallpox not only killed Wayna Qhapaq, it killed his son and designated heir-and his brother, uncle, and sister-wife. The main generals and much of the officer corps died, wrote the Inka chronicler Santacruz Pachacuti Yamqui Salcamayhua, "all their faces covered with scabs." So did the two regents left in Qosqo by Wayna Qhapaq to administer the empire. After the dying Wayna Qhapaq locked himself away so that nobody could see his pustulous face, Salcamayhua reported, he was visited by a terrifying midnight vision. Surrounding him in his dream were "millions upon millions of men." The Inka asked who they were. "Souls of the lost," the multitude told him. All of them "would die from the pestilence," each and every one.

The story is probably apocryphal, but its import isn't. Smallpox has an incubation period of about twelve days, during which time sufferers, who may not know they are sick, can infect anyone they meet. With its fine roads and great population movements, Tawantinsuyu was perfectly positioned for a major epidemic. Smallpox radiated throughout the empire like ink spreading through tissue paper. Millions of people simultaneously experienced its symptoms: high fever, vomiting, severe pain, oozing blisters everywhere on the body. Unable to number the losses, the Jesuit Martin de Murua said only that the toll was "infinite thousands."

The smallpox virus is thought to have evolved from a cattle virus that causes cowpox; a now-extinct equine virus responsible for horsepox; or, perhaps most likely, the camelpox virus, which affects camels, as the name suggests. People who survive the disease become immune to it. In Europe, the virus was such a constant presence that most adults were immune. Because the Western Hemisphere had no cows, horses, or camels, smallpox had no chance to evolve there. Indians had never been exposed to it-they were "virgin soil," in epidemiological jargon.

Virgin-soil death rates for smallpox are hard to establish because for the last century most potential research subjects have been vaccinated. But a study in the early 1960s of seven thousand unvaccinated smallpox cases in southern India found that the disease killed 43 percent of its victims. Noting the extreme vulnerability of Andean populations-they would not even have known to quarantine victims, as Europeans had-Dobyns hypothesized that the empire's population "may well have been halved during this epidemic." In about three years, that is, as many as one out of two people in Tawantinsuyu died.

The human and social costs are beyond measure. Such overwhelming traumas tear at the bonds that hold cultures together. The epidemic that struck Athens in 430 B.C., Thucydides reported, enveloped the city in "a great degree of lawlessness." The people "became contemptuous of everything, both sacred and profane." They joined ecstatic cults and allowed sick refugees to desecrate the great temples, where they died untended. A thousand years later the Black Death shook Europe to its foundations. Martin Luther's rebellion against Rome was a grandson of the plague, as was modern anti-Semitism. Landowners' fields were emptied by death, forcing them either to work peasants harder or pay more to attract new labor. Both choices led to social unrest: the Jacquerie (France, 1358), the Revolt of Ciompi (Florence, 1378), the Peasants' Revolt (England, 1381), the Catalonian Rebellion (Spain, 1395), and dozens of flare-ups in the German states. Is it necessary to spell out that societies mired in fratricidal chaos are vulnerable to conquest? To borrow a trope from the historian Alfred Crosby, if Genghis Khan had arrived with the Black Death, this book would not be written in a European language.

As for Tawantinsuyu, smallpox wiped out Wayna Qhapaq and his court, which led to civil war as the survivors contested the spoils. The soldiers who died in the battle between Atawallpa and Washkar were as much victims of smallpox as those who died from the virus itself.

The ferocity of the civil war was exacerbated by the epidemic's impact on a peculiarly Andean institution: royal mummies. People in Andean societies viewed themselves as belonging to family lineages. (Europeans did, too, but lineages were more important in the Andes; the pop-cultural comparison might be The Lord of the Rings, in which characters introduce themselves as "X, son of Y" or "A, of B's line.") Royal lineages, called panaqa, were special. Each new emperor was born in one panaqa but created a new one when he took the fringe. To the new panaqa belonged the Inka and his wives and children, along with his retainers and advisers. When the Inka died his panaqa mummified his body. Because the Inka was believed to be an immortal deity, his mummy was treated, logically enough, as if it were still living. Soon after arriving in Qosqo, Pizarro's companion Miguel de Estete saw a parade of defunct emperors. They were brought out on litters, "seated on their thrones and surrounded by pages and women with flywhisks in their hands, who ministered to them with as much respect as if they had been alive."

Because the royal mummies were not considered dead, their successors obviously could not inherit their wealth. Each Inka's panaqa retained all of his possessions forever, including his palaces, residences, and shrines; all of his remaining clothes, eating utensils, fingernail parings, and hair clippings; and the tribute from the land he had conquered. In consequence, as Pedro Pizarro realized, "the greater part of the people, treasure, expenses, and vices [in Tawantinsuyu] were under the control of the dead." The mummies spoke through female mediums who represented the panaqa's surviving courtiers or their descendants. With almost a dozen immortal emperors jostling for position, high-level Inka society was characterized by ramose political intrigue of a scale that would have delighted the Medici. Emblematically, Wayna Qhapaq could not construct his own villa on Awkaypata-his undead ancestors had used up all the available space. Inka society had a serious mummy problem.

After smallpox wiped out much of the political elite, each panaqa tried to move into the vacuum, stoking the passions of the civil war. Different mummies at different times backed different claimants to the Inka throne. After Atawallpa's victory, his panaqa took the mummy of Thupa Inka from its palace and burned it outside Qosqo-burned it alive, so to speak. And later Atawallpa instructed his men to seize the gold for his ransom as much as possible from the possessions of another enemy panaqa, that of Pachacuti's mummy.

Washkar's panaqa kept the civil war going even after his death (or, rather, nondeath). While Atawallpa was imprisoned, Washkar's panaqa sent one of his younger brothers, Thupa Wallpa, to Cajamarca. In a surreptitious meeting with Pizarro, Thupa Wallpa proclaimed that he was Washkar's legitimate heir. Pizarro hid him in his own quarters. Soon afterward, the lord of Cajamarca, who had backed Washkar in the civil war, told the Spanish that Atawallpa's army was on the move, tens of thousands strong. Its generals planned to attack Pizarro, he said, and free the emperor. Atawallpa denied the charge, truthfully. Pizarro nonetheless ordered him to be bound. Some of the Spaniards most sympathetic to Atawallpa asked to investigate. Soon after they left, two Inka ran to Pizarro, claiming that they had just fled from the invading army. Pizarro hurriedly convoked a military tribunal, which quickly sentenced the Inka to execution-the theory apparently being that the approaching army would not attack if its leader were dead. Too late the Spanish expedition came back to report that no Inka army was on the move. Thupa Wallpa emerged from hiding and was awarded the fringe as the new Inka.

The execution, according to John Rowe, the Berkeley archaeologist, was the result of a conspiracy among Pizarro, Thupa Wallpa, and the lord of Cajamarca. By ridding himself of Atawallpa and taking on Thupa Wallpa, Rowe argued, Pizarro "had exchanged an unwilling hostage for a friend and ally." In fact, Thupa Wallpa openly swore allegiance to Spain. To him, the oath was a small price to pay; by siding with Pizarro, Washkar's panaqa, "which had lost everything, had a chance again." Apparently the new Inka hoped to return with Pizarro to Qosqo, where he might be able to seize the wheel of state. After that, perhaps, he could wipe out the Spaniards.

Although Andean societies have been buffeted by disease and economic exploitation since the arrival of Europeans, indigenous tradition remained strong enough that this chicha seller in Cuzco, photographed by Martin Chambi in 1921, might have seemed unremarkable in the days of the Inka.

On the way to Qosqo, Pizarro met his first important resistance near the river town of Hatun Xauxa, which had been overrun by Atawallpa's army during the civil war. The same force had returned there to battle the Spanish. But the Inka army's plan to burn down the town and prevent the invaders from crossing the river was foiled by the native Xauxa and Wanka populace, which had long resented the empire. Not only did they fight the Inka, they followed the old adage about the enemy of my enemy being my friend and actually furnished supplies to Pizarro.

After the battle Thupa Wallpa suddenly died-so suddenly that many Spaniards believed he had been poisoned. The leading suspect was Challcochima, one of Atawallpa's generals, whom Pizarro had captured at Cajamarca and brought along on his expedition to Qosqo. Challcochima may not have murdered Thupa Wallpa, but he certainly used the death to try to persuade Pizarro that the next Inka should be one of Atawallpa's sons, not anyone associated with Washkar. Meanwhile, Washkar's panaqa sent out yet another brother, Manqo Inka. He promised that if he were chosen to succeed Thupa Wallpa he would swear the same oath of allegiance to Spain. In return, he asked Pizarro to kill Challcochima. Pizarro agreed and the Spaniards publicly burned Challcochima to death in the main plaza of the next town they came to. Then they rode toward Qosqo.

To Dobyns, the moral of this story was clear. The Inka, he wrote in his 1963 article, were not defeated by steel and horses but by disease and factionalism. In this he was echoing conclusions drawn centuries before by Pedro Pizarro. Had Wayna Qhapaq "been alive when we Spaniards entered this land," the conquistador remarked, "it would have been impossible for us to win it.... And likewise, had the land not been divided by the [smallpox-induced civil] wars, we would not have been able to enter or win the land."

Pizarro's words, Dobyns realized, applied beyond Tawantinsuyu. He had studied demographic records in both Peru and southern Arizona. In both, as in New England, epidemic disease arrived before the first successful colonists. When the Europeans actually arrived, the battered, fragmented cultures could not unite to resist the incursion. Instead one party, believing that it was about to lose the struggle for dominance, allied with the invaders to improve its position. The alliance was often successful, in that the party gained the desired advantage. But its success was usually temporary and the culture as a whole always lost.

Between the sixteenth and eighteenth centuries, this pattern occurred again and again in the Americas. It was a kind of master narrative of postcontact history. In fact, Europeans routinely lost when they could not take advantage of disease and political fragmentation. Conquistadors tried to take Florida half a dozen times between 1510 and 1560-and failed each time. In 1532 King Joo III of Portugal divided the coast of Brazil into fourteen provinces and dispatched colonists to each one. By 1550 only two settlements survived. The French were barely able to sustain trading posts in the St. Lawrence and didn't even try to plant their flag in pre-epidemic New England. European microorganisms were slow to penetrate the Yucatan Peninsula, where most of the Maya polities were too small to readily play off against each other. In consequence, Spain never fully subdued the Maya. The Zapatista rebellion that convulsed southern Mexico in the 1990s was merely the most recent battle in an episodic colonial war that began in the sixteenth century.

All of this was important, the stuff of historians' arguments and doctoral dissertations, but Dobyns was thinking of something else. If Pizarro had been amazed by the size of Tawantinsuyu after the terrible epidemic and war, how many people had been living there to begin with? Beyond that, what was the population of the Western Hemisphere in 1491?

AN ARITHMETICAL PROGRESSION.

Wayna Qhapaq died in the first smallpox epidemic. The virus struck Tawantinsuyu again in 1533, 1535, 1558, and 1565. Each time the consequences were beyond the imagination of our fortunate age. "They died by scores and hundreds," recalled one eyewitness to the 1565 outbreak. "Villages were depopulated. Corpses were scattered over the fields or piled up in the houses or huts.... The fields were uncultivated; the herds were untended [and] the price of food rose to such an extent that many persons found it beyond their reach. They escaped the foul disease, but only to be wasted by famine." In addition, Tawantinsuyu was invaded by other European pestilences, to which the Indians were equally susceptible. Typhus (probably) in 1546, influenza in 1558 (together with smallpox), diphtheria in 1614, measles in 1618-all flensed the remains of Inka culture. Taken as a whole, Dobyns thought, the epidemics must have killed nine out of ten of the inhabitants of Tawantinsuyu.

Dobyns was not the first to arrive at this horrific conclusion. But he was the first to put it together with the fact that smallpox visited before anyone in South America had even seen Europeans. The most likely source of the virus, Dobyns realized, was the Caribbean. Smallpox was recorded to have appeared on the island of Hispaniola in November or December 1518. It killed a third of the native population before jumping to Puerto Rico and Cuba. Spaniards, exposed in childhood to the virus, were mostly immune. During Hernan Cortes's conquest of Mexico, an expedition led by Panfilo de Narvaez landed on April 23, 1520, near what is today the city of Veracruz. According to several Spanish accounts, the force included an African slave named Francisco Eguia or Baguia who had smallpox. Other reports say that the carriers were Cuban Indians whom Narvaez had brought as auxiliaries. In any case, someone brought the virus-and infected a hemisphere.

The disease raced to Tenochtitlan, leading city of the Mexica (Aztecs), where it laid waste to the metropolis and then the rest of the empire. From there, Dobyns discovered, colonial accounts show smallpox hopscotching through Central America to Panama. At that point it was only a few hundred miles from the Inka frontier. The virus seemingly crossed the gap, with catastrophic consequences.

Then Dobyns went further. When microbes arrived in the Western Hemisphere, he argued, they must have swept from the coastlines first visited by Europeans to inland areas populated by Indians who had never seen a white person. Colonial writers knew that disease tilled the virgin soil of the Americas countless times in the sixteenth century. But what they did not, could not, know is that the epidemics shot out like ghastly arrows from the limited areas they saw to every corner of the hemisphere, wreaking destruction in places that never appeared in the European historical record. The first whites to explore many parts of the Americas therefore would have encountered places that were already depopulated.

As a result, Dobyns said, all colonial population estimates were too low. Many of them, put together just after epidemics, would have represented population nadirs, not approximations of precontact numbers. From a few incidents in which before and after totals are known with relative certainty, Dobyns calculated that in the first 130 years of contact about 95 percent of the people in the Americas died. To estimate native numbers before Columbus, one thus had to multiply census figures from those times by a factor of twenty or more. The results obtained by this procedure were, by historical standards, stunningly high.

Historians had long wondered how many Indians lived in the Americas before contact. "Debated since Columbus attempted a partial census at Hispaniola in 1496," Denevan, the Beni geographer, has written, "it remains one of the great inquiries of history." Early researchers' figures were, to put it mildly, informally ascertained. "Most of them weren't even ballpark calculations," Denevan told me. "No ballpark was involved." Only in 1928 did the first careful estimate of the indigenous population appear. James Mooney, a distinguished ethnographer at the Smithsonian Institution, combed through colonial writings and government documents to conclude that in 1491 North America had 1.15 million inhabitants. Alfred L. Kroeber, the renowned Berkeley anthropologist, built upon Mooney's work in the 1930s. Kroeber cut back the tally still further, to 900,000-a population density of less than one person for every six square miles. Just 8.4 million Indians, Kroeber suggested, had lived in the entire hemisphere.

Recognizing that his continent-wide estimate did not account for regional variation, Kroeber encouraged future scholars to seek out and analyze "sharply localized documentary evidence." As he knew, some of his Berkeley colleagues were already making those analyses. Geographer Carl Sauer published the first modern estimate of northwest Mexico's pre-Columbian population in 1935. Meanwhile, physiologist Sherburne F. Cook investigated the consequences of disease in the same area. Cook joined forces with Woodrow W. Borah, a Berkeley historian, in the mid-1950s. In a series of publications that stretched to the 1970s, the two men combed through colonial financial, census, and land records. Their results made Kroeber uneasy. When Columbus landed, Cook and Borah concluded, the central Mexican plateau alone had a population of 25.2 million. By contrast, Spain and Portugal together had fewer than ten million inhabitants. Central Mexico, they said, was the most densely populated place on earth, with more than twice as many people per square mile than China or India.

"Historians and anthropologists did not, however, seem to be paying much attention" to Cook and Borah, Dobyns wrote. Years later, his work, coupled with that of Denevan, Crosby, and William H. McNeill, finally made them take notice. Based on their work and his own, Dobyns argued that the Indian population in 1491 was between 90 and 112 million people. Another way of saying this is that when Columbus sailed more people lived in the Americas than in Europe.

According to a 1999 estimate from the United Nations, the earth's population in the beginning of the sixteenth century was about 500 million. If Dobyns was right, disease claimed the lives of 80 to 100 million Indians by the first third of the seventeenth century. All these numbers are at best rough approximations, but their implications are clear: the epidemics killed about one out of every five people on earth. According to W. George Lovell, a geographer at Queen's University in Ontario, it was "the greatest destruction of lives in human history."

Dobyns published his conclusions in the journal Current Anthropology in 1966. They spawned rebuttals, conferences, even entire books. (Denevan assembled one: The Native Population of the Americas in 1492.) "I always felt guilty about the impact of my Current Anthropology article," Dobyns told me, "because I thought and still think that Cook and Borah and Sauer had all said this in print earlier, but people weren't listening. I'm still puzzled by the reaction, to tell you the truth. Maybe it was the time-people were prepared to listen in the 1960s."

Listen-and attack. Dobyns's population projections were quickly seen by some as politically motivated-self-flagellation by guilty white liberals or, worse, a push to inflate the toll of imperialism from the hate-America crowd. "No question about it, some people want those higher numbers," Shepard Krech III, an anthropologist at Brown, told me. These people, he said, were thrilled when Dobyns revisited the subject in a 1983 book, Their Number Become Thinned, and revised his estimates upward.

Most researchers thought Dobyns's estimates too high but few critics were as vehement as David Henige, of the University of Wisconsin, whose book, Numbers from Nowhere, published in 1998, is a landmark in the literature of demographic vilification. "Suspect in 1966, it is no less suspect nowadays," Henige charged of Dobyns's work. "If anything, it is worse." Henige stumbled across a seminar on Indian demography taught by Denevan in 1976. An "epiphanic moment" occurred when he read that Cook and Borah had "uncovered" the existence of eight million people in Hispaniola. Can you just invent millions of people? he wondered. "We can make of the historical record that there was depopulation and movement of people from internecine warfare and diseases," he said to me. "But as for how much, who knows? When we start putting numbers to something like that-applying large figures like 95 percent-we're saying things we shouldn't say. The number implies a level of knowledge that's impossible."

Indian activists reject this logic. "You always hear white people trying to minimize the size of the aboriginal populations their ancestors personally displaced," according to Lenore Stiffarm, an ethnologist at the University of Saskatchewan. Dismissing the impact of disease, in her view, is simply a way to reduce the original population of the Americas. "Oh, there used to be a few people there, and disease killed some of them, so by the time we got here they were almost all gone." The smaller the numbers of Indians, she said, the easier it is to regard the continent as empty, and hence up for grabs. "It's perfectly acceptable to move into unoccupied land," Stiffarm told me. "And land with only a few 'savages' is the next best thing."

When Henige wrote Numbers from Nowhere, the fight about pre-Columbian population had already consumed forests' worth of trees-his bibliography is ninety pages long. Four decades after Dobyns's article appeared, his colleagues "are still struggling to get out of the crater that paper left in anthropology," according to James Wilson, author of Their Earth Shall Weep, a history of North America's indigenous peoples after conquest. The dispute shows no sign of abating. This is partly because of the inherent fascination with the subject. But it is also due to the growing realization of how much is at stake.

Frequently Asked Questions.

NOT ENOUGH FOR YANKEE STADIUM.

On May 30, 1539, Hernando De Soto landed his private army near Tampa Bay in Florida. De Soto was a novel figure: half warrior, half venture capitalist. He grew very rich very young in Spanish America by becoming a market leader in the nascent slave trade. The profits helped to fund the conquest of the Inka, which made De Soto wealthier still. He accompanied Pizarro to Tawantinsuyu, burnishing his reputation for brutality-he personally tortured Challcochima, Atawallpa's chief general, before his execution. Literally looking for new worlds to conquer, De Soto returned to Spain soon after his exploits in Peru. In Charles V's court he persuaded the bored monarch to let him loose in North America with an expedition of his own. He sailed to Florida with six hundred soldiers, two hundred horses, and three hundred pigs.

From today's perspective, it is difficult to imagine the ethical system that could justify De Soto's subsequent actions. For four years his force wandered through what are now Florida, Georgia, North and South Carolina, Tennessee, Alabama, Mississippi, Arkansas, Texas, and Louisiana, looking for gold and wrecking most everything it touched. The inhabitants often fought back vigorously, but they were baffled by the Spaniards' motives and astounded by the sight and sound of horses and guns. De Soto died of fever with his expedition in ruins. Along the way, though, he managed to rape, torture, enslave, and kill countless Indians. But the worst thing he did, some researchers say, was entirely without malice-he brought pigs.

According to Charles Hudson, an anthropologist at the University of Georgia who spent fifteen years reconstructing De Soto's path, the expedition built barges and crossed the Mississippi a few miles downstream from the present site of Memphis. It was a nervous time: every afternoon, one of the force later recalled, several thousand Indian soldiers approached in canoes to within "a stone's throw" of the Spanish and mocked them as they labored. The Indians, "painted with ochre," wore "plumes of many colors, having feathered shields in their hands, with which they sheltered the oarsmen on either side, the warriors standing erect from bow to stern, holding bows and arrows." Utterly without fear, De Soto ignored the taunts and occasional volleys of arrows and poled over the river into what is now eastern Arkansas, a land "thickly set with great towns," according to the account, "two or three of them to be seen from one." Each city protected itself with earthen walls, sizable moats, and deadeye archers. In his brazen fashion, De Soto marched right in, demanded food, and marched out.

After De Soto left, no Europeans visited this part of the Mississippi Valley for more than a century. Early in 1682 white people appeared again, this time Frenchmen in canoes. In one seat was Rene-Robert Cavelier, Sieur de la Salle. La Salle passed through the area where De Soto had found cities cheek by jowl. It was deserted-the French didn't see an Indian village for two hundred miles. About fifty settlements existed in this strip of the Mississippi when De Soto showed up, according to Anne Ramenofsky, an archaeologist at the University of New Mexico. By La Salle's time the number had shrunk to perhaps ten, some probably inhabited by recent immigrants. De Soto "had a privileged glimpse" of an Indian world, Hudson told me. "The window opened and slammed shut. When the French came in and the record opened up again, it was a transformed reality. A civilization crumbled. The question is, how did this happen?"

Today most historians and anthropologists believe the culprit was disease. In the view of Ramenofsky and Patricia Galloway, an anthropologist at the University of Texas, the source of contagion was very likely not De Soto's army but its ambulatory meat locker: his three hundred pigs. De Soto's company was too small to be an effective biological weapon. Sicknesses like measles and smallpox would have burned through his six hundred men long before they reached the Mississippi. But that would not have been true for his pigs.

Pigs were as essential to the conquistadors as horses. Spanish armies traveled in a porcine cloud; drawn by the supper trough, the lean, hungry animals circled the troops like darting dogs. Neither species regarded the arrangement as novel; they had lived together in Europe for millennia. When humans and domesticated animals share quarters, they are constantly exposed to each other's microbes. Over time mutation lets animal diseases jump to people: avian influenza becomes human influenza, bovine rinderpest becomes human measles, horsepox becomes human smallpox. Unlike Europeans, Indians did not live in constant contact with many animals. They domesticated only the dog; the turkey (in Mesoamerica); and the llama, the alpaca, the Muscovy duck, and the guinea pig (in the Andes). In some ways this is not surprising: the New World had fewer animal candidates for taming than the Old. Moreover, few Indians carry the gene that permits adults to digest lactose, a form of sugar abundant in milk. Non-milk drinkers, one imagines, would be less likely to work at domesticating milk-giving animals. But this is guesswork. The fact is that what scientists call zoonotic disease was little known in the Americas. By contrast, swine, mainstays of European agriculture, transmit anthrax, brucellosis, leptospirosis, trichinosis, and tuberculosis. Pigs breed exuberantly and can pass diseases to deer and turkeys, which then can infect people. Only a few of De Soto's pigs would have had to wander off to contaminate the forest.

The calamity wreaked by the De Soto expedition, Ramenofsky and Galloway argued, extended across the whole Southeast. The societies of the Caddo, on the Texas-Arkansas border, and the Coosa, in western Georgia, both disintegrated soon after. The Caddo had a taste for monumental architecture: public plazas, ceremonial platforms, mausoleums. After De Soto's army left the Caddo stopped erecting community centers and began digging community cemeteries. Between the visits of De Soto and La Salle, according to Timothy K. Perttula, an archaeological consultant in Austin, Texas, the Caddoan population fell from about 200,000 to about 8,500-a drop of nearly 96 percent. In the eighteenth century, the tally shrank further, to 1,400. An equivalent loss today would reduce the population of New York City to 56,000, not enough to fill Yankee Stadium. "That's one reason whites think of Indians as nomadic hunters," Russell Thornton, an anthropologist at the University of California at Los Angeles, said to me. "Everything else-all the heavily populated urbanized societies-was wiped out."

Could a few pigs truly wreak this much destruction? Such apocalyptic scenarios have invited skepticism since Henry Dobyns first drew them to wide attention. After all, no eyewitness accounts exist of the devastation-none of the peoples in the Southeast had any form of writing known today. Spanish and French narratives cannot be taken at face value, and in any case say nothing substantial about disease. (The belief that epidemics swept through the Southeast comes less from European accounts of the region than from the disparities among those accounts.) Although the archaeological record is suggestive, it is also frustratingly incomplete; soon after the Spaniards visited, mass graves became more common in the Southeast, but there is yet no solid proof that a single Indian in them died of a pig-transmitted disease. Asserting that De Soto's visit caused the subsequent collapse of the Caddo and Coosa may be only the old logical fallacy of post hoc ergo propter hoc.

Not only do archaeologists like Dobyns, Perttula, and Ramenofsky argue that unrecorded pandemics swept through the Americas, they claim that the diseases themselves were of unprecedented deadliness. As a rule, viruses, microbes, and parasites do not kill the majority of their victims-the pest that wipes out its host species has a bleak evolutionary future. The influenza epidemic of 1918, until AIDS the greatest epidemic of modern times, infected tens of millions around the world but killed fewer than 5 percent of its victims. Even the Black Death, a symbol of virulence, was not as deadly as these epidemics are claimed to be. The first European incursion of the Black Death, in 134751, was a classic virgin-soil epidemic; mutation had just created the pulmonary version of the bacillus Yersinia pestis. But even then the disease killed perhaps a third of its victims. The Indians in De Soto's path, if researchers are correct, endured losses that were anomalously greater. How could this be true? the skeptics ask.

Consider, too, the Dobynsesque procedure for recovering original population numbers: applying an assumed death rate, usually 95 percent, to the observed population nadir. According to Douglas H. Ubelaker, an anthropologist at the National Museum of Natural History, the population nadir for Indians north of the Rio Grande was around 1900, when their numbers fell to about half a million. Assuming a 95 percent death rate (which Ubelaker, a skeptic, does not), the precontact population of North America would have been 10 million. Go up 1 percent to a 96 percent death rate and the figure jumps to 12.5 million-creating more than two million people arithmetically from a tiny increase in mortality rates. At 98 percent, the number bounds to 25 million. Minute changes in baseline assumptions produce wildly different results.

Worse, the figures have enormous margins of error. Rudolph Zambardino, a statistician at North Staffordshire Polytechnic, in England, has pointed out that the lack of direct data forces researchers into salvos of extrapolation. To approximate the population of sixteenth-century Mexico, for example, historians have only the official counts of casados (householders) in certain areas. To calculate the total population, they must adjust that number by the estimated average number of people in each home, the estimated number of homes not headed by a casado (and thus not counted), the estimated number of casados missed by the census takers, and so on. Each one of these factors has a margin of error. Unfortunately, as Zambardino noted, "the errors multiply each other and can escalate rapidly to an unacceptable magnitude." If researchers presented their estimates with the proper error bounds, he said, they would see that the spread is far too large to constitute "a meaningful quantitative estimate."

Extraordinary claims require extraordinary evidence, scientists say. Other episodes of mass fatality are abundantly documented: the Black Death in Europe, the post-collectivization famine in the Soviet Union, even the traffic in African slaves. Much less data support the notion that Old World bacteria and viruses turned the New World into an abattoir.*10 Such evidence as can be found lies scribbled in the margins of European accounts-it is, as Crosby admitted, "no better than impressionistic."

"Most of the arguments for the very large numbers have been theoretical," Ubelaker told me. "But when you try to marry the theoretical arguments to the data that are available on individual groups in different regions, it's hard to find support for those numbers." Archaeologists, he said, keep searching for the settlements in which those millions of people supposedly lived. "As more and more excavation is done, one would expect to see more evidence for [dense populations] than has thus far emerged." Dean R. Snow, of Pennsylvania State, repeatedly examined precontact sites in eastern New York and found "no support for the notion that ubiquitous pandemics swept the region." In the skeptics' view, Dobyns, and other High Counters (as proponents of large pre-Columbian numbers have been called) are like people who discover an empty bank account and claim from its very emptiness that it once contained millions of dollars. Historians who project large Indian populations, Low Counter critics say, are committing the intellectual sin of arguing from silence.

Given these convincing rebuttals, why have the majority of researchers nonetheless become High Counters? In arguing that Indians died at anomalously high rates from European diseases, are researchers claiming that they were somehow uniquely vulnerable? Why hypothesize the existence of vast, super-deadly pandemics that seem unlike anything else in the historical record? The speed and scale of the projected losses "boggle the mind," observed Colin G. Calloway, a historian at Dartmouth-one reason, he suggested, that researchers were so long reluctant to accept them. Indeed, how can one understand losses of such unparalleled scope? And if the European entrance into the Americas five centuries ago was responsible for them, what moral reverberations does this have today?

THE GENETICS OF VULNERABILITY.

In August 1967 a missionary's two-year-old daughter came down with measles in a village on the Toototobi River in Brazil, near the border with Venezuela. She and her family had just returned from the Amazonian city of Manaus and had been checked and cleared by Brazilian doctors before departure. Nonetheless the distinctive spots of measles emerged a few days after the family's arrival on the Toototobi. The village, like many others in the region, was populated mainly by Yanomami Indians, a forest society on the Brazil-Venezuela border that is among the least Westernized on earth. They had never before encountered the measles virus. More than 150 Yanomami were in the village at the time. Most or all caught the disease. Seventeen died despite the horrified missionaries' best efforts. And the virus escaped and spread throughout the Yanomami heartland, carried by people who did not know they had been exposed.

Partly by happenstance, the U.S. geneticist James Neel and the U.S. anthropologist Napoleon Chagnon flew into Yanomami country in the midst of the epidemic. Neel, who had long been worried about measles, was carrying several thousand doses of vaccine. Alas, the disease had preceded them. They frantically tried to create an epidemiological "firebreak" by vaccinating ahead of the disease. Despite their efforts, the affected villages had a mean death rate of 8.8 percent. Almost one out of ten people died from a sickness that in Western societies was just a childhood annoyance.

Later Neel concluded that the high death rate was in part due to grief and despair, rather than the virus itself. Still, the huge toll was historically unprecedented. The implication, implausible at first glance, was that Indians in their virgin-soil state were more vulnerable to European diseases than virgin-soil Europeans would have been. Perhaps surprisingly, there is some scientific evidence that Native Americans were for genetic reasons unusually susceptible to foreign microbes and viruses-one reason that researchers believe that pandemics of Dobynsian scale and lethality could have occurred.

Here I must make a distinction between two types of susceptibility. The first is the lack of acquired immunity-immunity gained from a previous exposure to a pathogen. People who have never had chicken pox are readily infected by the virus. After they come down with the disease, their immune system trains itself, so to speak, to fight off the virus, and they never catch it again, no matter how often they are exposed. Most Europeans of the day had been exposed to smallpox as children, and those who didn't die were immune. Smallpox and other European diseases didn't exist in the Americas, and so every Indian was susceptible to them in this way.

In addition to having no acquired immunity (the first kind of vulnerability), the inhabitants of the Americas had immune systems that some researchers believe were much more restricted than European immune systems. If these scientists are correct, Indians as a group had less innate ability to defend themselves against epidemic disease (the second kind of vulnerability). The combination was devastating.

The second type of vulnerability stems from a quirk of history. Archaeologists dispute the timing and manner of Indians' arrival in the Americas, but almost all researchers believe that the initial number of newcomers must have been small. Their gene pool was correspondingly restricted, which meant that Indian biochemistry was and is unusually homogeneous. More than nine out of ten Native Americans-and almost all South American Indians-have type O blood, for example, whereas Europeans are more evenly split between types O and A.

Evolutionarily speaking, genetic homogeneity by itself is neither good nor bad. It can be beneficial if it means that a population lacks deleterious genes. In 1491, the Americas were apparently free or almost free of cystic fibrosis, Huntington's chorea, newborn anemia, schizophrenia, asthma, and (possibly) juvenile diabetes, all of which have some genetic component. Here a limited gene pool may have spared Indians great suffering.

Genetic homogeneity can be problematic, too. In the 1960s and 1970s Francis L. Black, a virologist at Yale, conducted safety and efficacy tests among South American Indians of a new, improved measles vaccine. During the tests he drew blood samples from the people he vaccinated, which he later examined in the laboratory. When I telephoned Black, he told me that the results were "thought-provoking." Every individual person's immune system responded robustly to the vaccine. But the native population as a whole had a "very limited spectrum of responses." And that, he said, "could be a real problem in the right circumstances." For Indians, those circumstances arrived with Columbus.

Black was speaking of human leukocyte antigens (HLAs), molecules inside most human cells that are key to one of the body's two main means of defense. Cells of all sorts are commonly likened to biochemical factories, busy ferments in which dozens of mechanisms are working away in complex sequences that are half Rube Goldberg, half ballet. Like well-run factories, cells are thrifty; part of the cellular machinery chops up and reuses anything that is floating around inside, including bits of the cell and foreign invaders such as viruses. Not all of the cut-up pieces are recycled. Some are passed on to HLAs, special molecules that transport the snippets to the surface of the cell.

Outside, prowling, are white blood cells-leukocytes, to researchers. Like minute scouts inspecting potential battle zones, leukocytes constantly scan cell walls for the little bits of stuff that HLAs have carried there, trying to spot anything that doesn't belong. When a leukocyte spots an anomaly-a bit of virus, say-it destroys the infected or contaminated cell immediately. Which means that unless an HLA lugs an invading virus to where the leukocyte can notice it, that part of the immune system cannot know it exists, let alone attack it.

HLAs carry their burdens to the surface by fitting them into a kind of slot. If the snippet doesn't fit into the slot, the HLA can't transport it, and the rest of the immune system won't be able to "see" it. All people have multiple types of HLA, which means that they can bring almost every potential problem to the attention of their leukocytes. Not every problem, though. No matter what his or her genetic endowment, no one person's immune system has enough different HLAs to identify every strain of every virus. Some things will always escape notice. Imagine someone sneezing in a crowded elevator, releasing into the air ten variants of a rhinovirus, the kind of virus that causes the common cold. (Viruses mutate quickly and are commonly present in the body in multiple forms, each slightly different from the others.) For simplicity's sake, suppose that the other elevator passengers inhale all ten versions of the virus. One man is lucky: he happens to have HLAs that can lock onto and carry pieces of all ten variants to the cell surface. Because his white blood cells can identify and destroy the infected cells, this man doesn't get sick. Not so lucky is the woman next to him: she has a different set of HLAs, which are able to pick up and transport only eight of the ten varieties. The other two varieties escape the notice of her leukocytes and go on to give her a howling cold (eventually other immune mechanisms kick in and she recovers). These disparate outcomes illustrate the importance to a population of having multiple HLA profiles; one person's HLAs may miss a particular bug, but another person may be equipped to combat it, and the population as a whole survives.

Most human groups are a scattershot mix of HLA profiles, which means that almost always some people in the group will not get sick when exposed to a particular pathogen. Indeed, if laboratory mice have too much HLA diversity, Black told me, researchers can't use them to observe the progress of an infectious disease. "You get messy results-they don't all get sick." The opposite is true as well, he said. People with similar HLA profiles fall victim to the same diseases in the same way.

In the 1990s Black reviewed thirty-six studies of South American Indians. Not to his surprise, he discovered that overall Indians have fewer HLA types than populations from Europe, Asia, and Africa. European populations have at least thirty-five main HLA classes, whereas Indian groups have no more than seventeen. In addition, Native American HLA profiles are dominated by an unusually small number of types. About one third of South American Indians, Black discovered, have identical or near-identical HLA profiles; for Africans the figure is one in two hundred. In South America, he estimated, the minimum probability that a pathogen in one host will next encounter a host with a similar immune spectrum is about 28 percent; in Europe, the chance is less than 2 percent. As a result, Black argued, "people of the New World are unusually susceptible to diseases of the Old."*11 Actually, some Old World populations were just as vulnerable as Native Americans to those diseases, and likely for the same reason. Indians' closest genetic relatives are indigenous Siberians. They did not come into substantial contact with Europeans until the sixteenth century, when Russian fur merchants overturned their governments, established military outposts throughout the region, and demanded furs in tribute. In the train of the Russian fur market came Russian diseases, notably smallpox.

The parallels with the Indian experience are striking. In 1768 the virus struck Siberia's Pacific coast, apparently for the first time. "No one knows how many have survived," confessed the governor of Irkutsk, the Russian base on Lake Baikal, apparently because officials were afraid to travel to the affected area. A decade later, in 1779, the round-the-globe expedition of Captain James Cook reached Kamchatka, the long peninsula on the Pacific coast. The shoreline, the British discovered, was a cemetery. "We every where met with the Ruins of large Villages with no Traces left of them but the Foundation of the Houses," lamented David Samwell, the ship's surgeon. "The Russians told us that [the villages] were destroyed by the small Pox." The explorer Martin Sauer, who visited Kamchatka five years after Cook's expedition, discovered that the Russian government had at last ventured into the former epidemic zone. Scarcely one thousand natives remained on the peninsula, according to official figures; the disease had claimed more than five thousand lives. The tally cannot be taken as exact, but the fact remains: a single epidemic killed more than three of every four indigenous Siberians in that area.

After a few such experiences, the natives tried to fight back. "As soon as [indigenous Siberians] learn that smallpox or other contagious diseases are in town," the political exile Heinrich von Fuch wrote, "they set up sentries along all the roads, armed with bows and arrows, and they will not allow anyone to come into their settlements from town. Likewise, they will not accept Russian flour or other gifts, lest these be contaminated with smallpox." Their efforts were in vain. Despite extreme precautions, disease cut down native Siberians again and again.

After learning about this sad history I again telephoned Francis Black. Being genetically determined, Indian HLA homogeneity cannot be changed (except by intermarriage with non-Indians). Did that mean that the epidemics were unavoidable? I asked. Suppose that the peoples of the Americas had, in some parallel world, understood the concept of contagion and been prepared to act on it. Could the mass death have been averted?

"There have been lots of cases where individual towns kept out epidemics," Black said. During plague episodes, "medieval cities would barricade themselves behind their walls and kill people who tried to come in. But whole countries-that's much harder. England has kept out rabies. That's the biggest success story that comes to mind, offhand. But rabies is primarily an animal disease, which helps, because you only have to watch the ports-you don't have many undocumented aliens sneaking in with sick dogs. And rabies is not highly contagious, so even if it slips through it is unlikely to spread."

He stopped speaking for long enough that I asked him if he was still on the line.

"I'm trying to imagine how you would do it," he said. "If Indians in Florida let in sick people, the effects could reach all the way up to here in Connecticut. So all these different groups would have had to coordinate the blockade together. And they'd have to do it for centuries-four hundred years-until the invention of vaccines. Naturally they'd want to trade, furs for knives, that kind of thing. But the trade would have to be conducted in antiseptic conditions."

The Abenaki sent goods to Verrazzano on a rope strung from ship to shore, I said.

"You'd have to have the entire hemisphere doing that. And the Europeans would presumably have to cooperate, or most of them, anyway. I can't imagine that happening, actually. Any of it."

Did that mean the epidemics were inevitable and there was nothing to be done?

The authorities, he replied, could "try to maintain isolation, as I was saying. But that ends up being paternalistic and ineffective. Or they can endorse marriage and procreation with outsiders, which risks destroying the society they supposedly are trying to preserve. I'm not sure what I'd recommend. Except getting these communities some decent health care, which they almost never have."

Except for death, he went on, nothing in medicine is inevitable. "But I don't see how it [waves of epidemics from European diseases] could have been prevented for very long. That's a terrible thought. But I've been working with highly contagious diseases for forty years, and I can tell you that in the long run it is almost impossible to keep them out."*12 "OUR EYES WERE APPALLED WITH TERROR"

A second reason historians believe that epidemics tore through Native American communities before Europeans arrived is that epidemics also did it after Europeans arrived. In her book Pox Americana (2001), the Duke University historian Elizabeth Fenn meticulously pieced together evidence that the Western Hemisphere was visited by two smallpox pandemics shortly before and during the Revolutionary War. The smaller of the two apparently began outside Boston in early 1774 and lurked in the area for the next several years like a sniper, picking off victims at the rate of ten to thirty a day. In Boston the Declaration of Independence was overshadowed by the previous day's proclamation of a citywide campaign of inoculation (an early, risky form of vaccination in which people deliberately infected themselves with a mild dose of smallpox to produce immunity).

Even as it besieged Boston, the virus also spread down the eastern seaboard, laying waste as far as Georgia. It wreaked havoc on the Ani Yun Wiya (the group often called the Cherokee, which is a mildly insulting name coined by their enemies, the Creek confederation) and the Haudenosaunee (the indigenous name for the six nations that made up what Europeans called the Iroquois League). Both were important allies of the British, and after the epidemic neither was able to fight the colonists successfully. Smallpox also ruined the British plan to raise an army of slaves and indentured servants by promising them freedom after the war-the disease killed off most of the "Ethiopian regiment" even as it assembled.

An equal-opportunity killer, smallpox ravaged the rebels, too. The virus had been endemic in Europe for centuries, which meant that most Europeans were exposed to it before adulthood. But it was only an occasional, terrible visitor in the Americas, which meant that most adult colonists had not acquired childhood immunity. On an individual level, they were almost as vulnerable as Indians. On a group level, though, they were less genetically homogeneous, which conferred some relative advantage; the virus would sweep through them, but not kill quite so many. Still, so many soldiers in the Continental army fell during the epidemic that revolutionary leaders feared that the disease would bring an end to their revolt. "The small Pox! The small Pox!" John Adams wrote to his wife, Abigail. "What shall We do with it?" His worries were on target: the virus, not the British, stopped the Continental army's drive into Quebec in 1776. In retrospect, Fenn told me, "One of George Washington's most brilliant moves was to inoculate the army against smallpox during the Valley Forge winter of '78." Without inoculation, she said, the smallpox epidemic could easily have handed the colonies back to the British.

Even as the first outbreak faded, Fenn wrote, a second, apparently unrelated epidemic burned through Mexico City. The first cases occurred in August 1779. By year's end perhaps eighteen thousand had died in the city area and the disease was racing through the countryside in every direction. Communications in those days were too poor to permit us to document a transmission chain, but records show smallpox flaring in separate explosions to the south like a chain of firecrackers: Guatemala (178081), Colombia (178183), Ecuador (1783). Was the virus retracing a journey to Tawantinsuyu it had taken before? "It seems likely," decided Calloway, the Dartmouth historian. Fenn tried to trace the virus as it went north. Like Dobyns, she examined parish burial records. In 1780 a telltale surge of mortality traveled north along the heavily traveled road to Santa Fe. From there, smallpox apparently exploded into most of western North America.

First to suffer, or so the sketchy evidence suggests, were the Hopi. Already reeling from a drought, they were blasted by smallpox-as many as nine out of ten may have died. When the Spanish governor tried to recruit the Hopi to live in missions, their leaders told him not to bother: the epidemic soon would expunge them from the earth. As if drought and contagion were not enough, the Hopi were constantly under attack by the Nermernuh (or Nemene), a fluid collection of hunting bands known today as the Comanche (the name, awarded by an enemy group, means "people who fight us all the time"). Originally based north of Santa Fe, the Nermernuh were on their way to dominating the southern plains; they had driven away their Apache and Hopi rivals with trip-hammer ambushes and deadly incursions and were bent on doing the same to any European colonists who ventured in. In 1781 the raiding abruptly stopped. Silence for eighteen months. Was the ceasefire due to Mexico City smallpox that had been transmitted by the Hopi? Four years afterward, a traveler noted in his diary that the Nermernuh lived in fear of disease because they had been recently struck by smallpox-tenuous but suggestive evidence.

What is certain is that both Hopi and Nermernuh were part of a network of exchange that had hummed with vitality since ancient times and had recently grown more intense with the arrival of horses, which sped up communication. Smallpox raced along the network through the Great Plains and the Rocky Mountains, ricocheting among the Mandans, Hidatsas, Ojibwes, Crows, Blackfoot, and Shoshone, a helter-skelter progress in which a virus leapfrogged from central Mexico to the shore of Hudson Bay in less than two years. Indians in the northern Great Plains kept "winter counts," oral chronologies of the most important events in each year. Often the counts were accompanied by a spiraling sequence of drawings on a hide, with each year summarized by a drawing as an aide-memoire. In several Lakota (Sioux) counts 178081 was bleakly summed as the year of Smallpox Used Them Up; and the Lakota were not the only ones affected.

In 1781 a company of Blackfoot stumbled across a Shoshone camp at dawn near the Red Deer River in Alberta. The Blackfoot were a tightly organized confederation of groups that inhabited the plains between the Missouri and Saskatchewan Rivers. Equipped with guns and horses from French traders, they had pushed their southern neighbors, the Shoshone-left at a disadvantage because they had no access to the French and their goods, and the Spanish, whom they did have access to, tried to block Indian access to weapons-from the plains into the mountains of what are now Wyoming and Colorado. When the Shoshone finally obtained guns-they traded with their linguistic cousins, the Nermernuh, who took the weapons as booty from defeated Spaniards-open warfare broke out. In this bellicose context, the Blackfoot party knew exactly what to do when it happened upon a slumbering Shoshone encampment. With "sharp flat daggers and knives," one of the raiders later remembered, they silently sliced open the Shoshone tents "and entered for the fight; but our war whoops instantly stopt, our eyes were appalled with terror; there was no one to fight with but the dead and the dying, each a mass of corruption." The Blackfoot did not touch the bodies, but were infected anyway. When the company returned home, the raider lamented, smallpox "spread from one tent to another as if the Bad Spirit carried it."

According to Fenn, "the great preponderance of the evidence" indicates that the Shoshone also transmitted smallpox down the Columbia River into the Pacific Northwest. Calloway suggests the Crow as a plausible alternative. Whoever passed on the virus, its effects were still visible a decade later in 1792, when the British navigator George Vancouver led the first European expedition to survey Puget Sound. Like Cook's crew in Kamchatka, he found a charnel house: deserted villages, abandoned fishing boats, human remains "promiscuously scattered about the beach, in great numbers." Everything they saw suggested "that at no very remote period this country had been far more populous than at present." The few suffering survivors, noted Second Lieutenant Peter Puget, were "most terribly pitted...indeed many have lost their Eyes."

Europeans were well versed in the brutal logic of quarantine. When plague appeared, they boarded up houses and fled to the countryside. By contrast, the historian Neal Salisbury observed, family and friends in Indian New England gathered at the sufferer's bedside to wait out the illness, a practice that "could only have served to spread the disease more rapidly." Even the idea of contagion itself was novel. "We had no belief that one Man could give [a disease] to another," the Blackfoot raider remembered, "any more than a wounded Man could give his wound to another." Because they knew of no protective measures, the toll was even higher than it would have been.

Living in the era of antibiotics, we find it difficult to imagine the simultaneous deaths of siblings, parents, relatives, and friends. As if by a flash of grim light, Indian villages became societies of widows, widowers, and orphans; parents lost their children, and children were suddenly alone. Rare is the human spirit that remains buoyant in a holocaust. "My people have been so unhappy for so long they wish to disincrease, rather than to multiply," a Paiute woman wrote in 1883. A Lakota winter count memorialized the year 1784 with a stark image: a pox-scarred man, alone in a tipi, shooting himself.

Disease not only shattered the family bonds that were the underlying foundation of Indian societies, it wiped out the political superstructure at the top. King Liholiho Kamehameha II and Queen Kamamalu of Hawai'i visited Great Britain on a diplomatic mission in 1824. While staying in a posh London hotel and attending the theater in the English king's own box, the royal couple and most of the rest of their party came down with measles. It killed the queen on July 8. The grieving king died six days later, at the age of twenty-seven. The death of the royal couple ushered in a time of social chaos. It was as catastrophic for Hawai'i as the death of Wayna Qhapaq for Tawantinsuyu.

A particularly poignant loss occurred in the summer of 1701, when the leaders of forty native nations convened in Montreal to negotiate an end to decades of war among themselves and the French. Death stalked the congress in the form of influenza. By then the Indians of the Northeast knew such diseases all too well: sickness had carried off so many members of the Haudenosaunee that the alliance was forced to replenish itself by adopting abductees and prisoners of war. At the time of the conference at least a quarter of the Haudenosaunee were former captives. At great personal risk, many Indian leaders attended the conference even after they knew that influenza was in Montreal. Dozens died. Among them was the Huron leader Kondiaronk, a famed orator who had, more than any other, convened the gathering as a last-ditch effort to avoid internecine conflict. His body was placed on a bed of beaver pelts, covered by a scarlet cloth, and surrounded by a copper pot, a rifle, and a sword. In their diversity, the objects symbolized the peaceful mixing of cultures that Kondiaronk hoped lay in the future.

Nobody knows how many died during the pandemics of the 1770s and 1780s, but even if one had a number it wouldn't begin to tally the impact. Disease turned whole societies to ash. Six Cree groups in western Canada disappeared after 1781; the Blackfoot nation, blasted by smallpox, sent peace emissaries to Shoshone bands, only to find that all had vanished. "The country to the south was empty and silent," Calloway wrote. So broken were the Omaha by disease that according to tradition they launched a deliberately suicidal attack against their enemies. Those who did not die quit their villages and became homeless wanderers.

Cultures are like books, the anthropologist Claude Levi-Strauss once remarked, each a volume in the great library of humankind. In the sixteenth century, more books were burned than ever before or since. How many Homers vanished? How many Hesiods? What great works of painting, sculpture, architecture, and music vanished or never were created? Languages, prayers, dreams, habits, and hopes-all gone. And not just once, but over and over again. In our antibiotic era, how can we imagine what it means to have entire ways of life hiss away like steam? How can one assay the total impact of the unprecedented calamity that gave rise to the world we live in? It seems important to try. I would submit that the best way to come near to encompassing the scale and kind of the loss, and its causes, is to look at the single case where the intellectual life of a Native American society is almost as well documented as its destruction.