On October 20, 1804, the Corps of Discovery camped just below the point where the Heart River empties into the Missouri, in present-day central North Dakota. Lewis and Clark were only a few months into their journey, and each day brought new wonders for the three-dozen men charged with exploring the lands acquired from France in the Louisiana Purchase. For William Clark, writing in his journal, the memorable sights of that autumn day in 1804 consisted mainly of animal migrations. But he took special notice of “an old Village of the Mandans,” which he soon learned had been abandoned by its residents after a smallpox epidemic had wreaked havoc among them in 1781. The Corps of Discovery wound up spending their first winter among the Indians at the Mandans’ new settlements a few miles upstream.

These two historical events—smallpox epidemics and the expedition of Lewis and Clark—are all that most Americans (scholars among them) know about these people of the Upper Missouri, if they have heard of them at all. This despite the fact that for more than two centuries, the thriving culture of the Mandans stood very near the heart of the world, in more ways than one: their homeland lies some 100 miles south of the geographic center of North America, and it was there that they established a vital trading center that reached as far as Hudson’s Bay, the southern Plains, and the Pacific Northwest. In her dazzling and compulsively readable new book, historian Elizabeth Fenn narrates the sweep of the Mandan past, focusing especially on the period from 1600-1838, when another smallpox epidemic nearly extinguished them altogether.

It is apt that Fenn should turn her considerable talents to the Mandans, given that her first book, Pox Americana, is a continental history of the smallpox epidemic of 1775-82, which erupted in Mexico City and barreled northward, killing more than 100,000 people and immiserating untold others. But Encounters at the Heart of the World shows readers that there is much more to Mandan history than merely their suffering at the hands of Euroamerican epidemiology. After all, it was their very success as a densely settled people at the center of a vast commercial nexus on the Missouri River that placed them time and again in the crosshairs of such diseases, to say nothing of their native enemies, who alternately traded with and raided them.

Fenn relies upon deep archival research and a felicitous prose style to bring this forgotten world to life, starting with the Mandans’ ancestral migrations from places south and east before their coalescence around the year 1400 in a fifty-mile stretch along the Missouri between the mouths of the Knife and Cannonball rivers. And what a rich and vibrant culture it was. Some of Fenn’s best work concerns the material and social life of the Mandans. Take, for instance, their distinctive earth lodges, stout post-and-beam structures built atop cache pits stuffed with corn, for which they became known and valued until this resource was destroyed by another pest introduced by Euroamericans: the Norway rat.

Although to the newcomers these clustered houses looked hastily and poorly arranged, with no right-angled streets or alleys, the irregular design was both deliberate and ingenious, as it helped disorient war parties launched by their rivals, chief among them the Lakota Sioux, who—because of their horse-bound nomadism—had escaped some of the worst ravages of smallpox and thus beset the more sedentary Mandans. Disease and warfare caused the Mandans to desert many of these well situated and fortified sites, the haunting remains of which are still visible today as clusters of circular depressions in the earth at scattered sites throughout North Dakota.

Perhaps the most compelling portion of the book is Fenn’s recreation of Mandan cosmology and religious life, particularly the Okipa ceremony, an elaborate and intricate ritual performed every summer and which bore a strong resemblance—seen in fasting, gift exchange, and especially mortification of the flesh—to the Sun Dance, an annual ceremony of many other Plains groups. The artist George Catlin drew several scenes based on his observation of the four-day ceremony in July 1832, including one sketch depicting young warriors suspended from the ceiling of a ceremonial earth lodge by skewers dug into their chests, weighed down with buffalo skulls dangling from their backs. Fenn tells also of a distinct but related ritual, called “Walking with the Buffaloes,” in which young married women had sex with elderly male members of a respected tribal society, the Buffalo Bulls; the performance of this sacred rite was intended to bring herds of bison nearby so that Mandan hunters could provision their villages.

It is tricky indeed for scholars—native but especially otherwise—to gain access to such information and then to use it with accuracy and care. Fenn has surely done this, guided in no small part by her fascination with the Mandan world and her obvious affection for its living descendants. Fenn’s enthusiasm for her subject is on display right from the start, as in her preface—and then in short interludes sprinkled throughout the text—she tells us of her own encounters with the North Dakota landscape and the people who inhabited it. She has even drawn the maps for her own book. In her acknowledgements Fenn showers gratitude upon her many informants, among them Cedric Red Feather, who in 2011 facilitated the first Okipa ceremony in at least 122 years, with Fenn as an observer. If such generous inclusion has given her story added power, it has not compromised her ability to tell a balanced story; hers is an admiring but not romanticized account of the Mandans.

But neither is it a story of simple declension. Rather, Encounters at the Heart of the World is a tale of risings and fallings … and risings again. After the devastation of the 1781 smallpox epidemic, the surviving Mandans improvised by settling near their sometime-rivals, the Hidatsas, with whom they alternately cooperated and feuded, tensions stemming usually from commercial access to outsiders, whether overland British traders from Canada or Americans coming upriver from St. Louis. And the Mandans endured a second, and still worse, visitation from smallpox in 1837-38, which cut their numbers to 300, a rate of depopulation around 90%.

Given this tiny pool of survivors, a skeptic might ask why the story of the Mandans should matter to the contemporary reader? Unlike, say, the Sioux or the Comanches, who resisted U.S. expansion until after the Civil War, the Mandans posed no such threat (and in fact were unfailingly hospitable to American visitors). Among many possible reasons, several stand out, beginning with the satisfaction of learning about a now obscure people who played such a critical role in a land we think we know well. Moreover, the Mandan story is a reminder that even the most flourishing societies can be brought low, in virtually an instant, by the unpredictable workings of the natural world (to say nothing of human foes). But Fenn’s account tells us also that cultures can persist and even recover in the wake of such awful devastation.