INVESTIGATING THE VACANT QUARTER

The highlighted section of this map shows the area that archaeologist Stephen Williams called the Vacant Quarter. The red dots denote sites that were recently investigated by Charles Cobb and his team, or previously investigated by other archaeologists. The data from the previously investigated sites informed Cobb’s work. There are other sites that aren’t shown on the map that define the Vacant Quarter’s boundaries.

In the mid 1400s, Native Americans largely abandoned a large section of the central United States. Archaeologists, with a little help from an eighteenth-century cleric, have launched a new effort to understand why.

By David Malakoff

In 1978, archaeologist Stephen Williams was touring ancient settlement sites around the confluence of the Mississippi and Ohio rivers when an intriguing “notion came to me,” he later recalled. Williams, a Harvard University professor who had worked in the Central and Southeastern United States for decades, knew that the archaeological evidence showed that many of the sites had hosted thriving communities, some with thousands of people, during the Mississippian Period, which lasted from roughly A. D. 800 to 1550. Some featured the huge earthen ceremonial mounds that were a hallmark of Mississippian peoples. But Williams was also aware of a growing number of studies suggesting that

In 1939, a huge Works Progress Administration crew began their excavation of Angel Mounds, one of the better known sites in the Vacant Quarter. The crew uncovered more than two million artifacts.

people had abandoned many of the sites at roughly the same time, beginning in the mid-1400s. And when he sketched a map of the abandoned settlements, he realized they formed a vast area he called the Vacant Quarter, which covered some 50,000 square miles across eight states. It included some of the region’s largest and most studied Mississippian sites, including Cahokia in western Illinois and the Angel Mounds in Indiana, and also lesser-known sites far to the south in Tennessee, Alabama, and Mississippi.

When Williams, who died in 2017, first published his Vacant Quarter hypothesis in 1983, he was careful to note that he wasn’t proposing that the region became totally devoid of people. Some Native Americans likely still hunted and gathered food there. But the Vacant Quarter no longer had any “year-round settled villages,” he wrote, even as communities flourished around its perimeter. Indeed, the void appeared to represent the “burned out center” of the Late Mississippian period. And the abandonment could help explain why the first Europeans to visit the area, who arrived in the 1500s, reported finding derelict villages marked by an “echoing stillness.”

At first, many archaeologists were skeptical of the Vacant Quarter hypothesis. Over time, however, it steadily gained acceptance as researchers documented additional Late Mississippian sites in the region that appeared to have abruptly shifted from vibrant to vacant. But thirty-five years after Williams first presented his provocative ideas, archaeologists are still trying to answer some fundamental questions about the Vacant Quarter: What caused so many people to flee such a vast, bountiful area in just a generation or two? When did they leave? And where did they go?

Intent on answering some of those questions, researchers from three universities and the Chickasaw Nation have embarked on a new study of sites in central Tennessee and northern Mississippi that are on ancestral Chickasaw lands. By conducting new digs at one Mississippian mound, radiocarbon dating nearly 200 carbonized botanical remains in museum collections, and analyzing ceramics and ancient climate records, the researchers hope to get “a very fine resolution look at what was happening—socially, ecologically, and climatically—in these two very different parts of the Vacant Quarter in the century or so before abandonment,” said archaeologist Charles Cobb of the University of Florida, who is leading the study. “We want to know: Did [abandonment] happen the same way across the Vacant Quarter? Was it a slow, protracted process? Or was there some pivotal event that was the straw that broke the camel’s back?” The researchers will “zoom in very close on a handful of sites, but also zoom out to see how they fit into a much larger pattern,” added archaeologist Tony Boudreaux of the University Mississippi, who is also involved in the project.

The archaeologists are also getting some help from an unusual source: a Presbyterian minister named Thomas Bayes. Though Bayes has been dead for 250 years, he invented an innovative statistical approach that is still very much alive, and the researchers said it should enable them to develop

a clearer picture of when Mississippian peoples occupied some Vacant Quarter settlements, and when they left. “This will be one of the biggest deployments yet of Bayesian chronological techniques in American archaeology,” said Tony Krus of the University of South Dakota, who is leading that part of the project. “And it could be a game changer.” A ncient abandonments have long held “a particular fascination” for archaeologists, Cobb, Krus and their colleagues noted in a description of their Vacant Quarter project written for the National Science Foundation, a major funder of this multi-year endeavor. In the Southwestern United States, for instance, researchers have spent a century

Researchers from the Chickasaw Nation and the University of Mississippi water-screen ecavated dirt in search of tiny artifacts.

seeking to understand why, in the late thirteenth century, the Ancestral Puebloans vacated the spectacular cliff dwellings and stone cities they had built in the Mesa Verde region. It’s a mystery that has captivated the public, too, spawning countless books, magazine articles, and television shows.

But the idea that similarly dramatic mass departures once occurred in the Southeastern U.S. has traditionally gotten less attention from scholars and the media. In part, that may be because an abandoned, brush-covered dirt mound makes for less dramatic and colorful storytelling than a crumbling cliff dwelling. But Williams’ hypothesis “really helped focus attention on the idea that … there was something big going on in this region that we should be looking at,” recalled archaeologist David Anderson of University of Tennessee, who has studied the Vacant Quarter, but is not involved in this project.

In several papers Williams even suggested how researchers could go about testing whether the Vacant Quarter was, in fact, a real thing. One issue he flagged was that much of the evidence supporting the idea came from prehistoric sites located in river valleys. Perhaps, he wrote, whatever forces had prompted people to abandon these low-lying settlements, such as floods, warfare, or disease, hadn’t affected Mississippian communities located on higher ground or further away from river valleys. Williams challenged researchers to see if this notion was correct.

In the early 1990s, Cobb was one archaeologist who accepted that challenge. Over a decade, he and his colleagues documented three Late Mississippian villages—known as Dillow’s Ridge, Millstone Bluff, and Hayes Creek—that were located on uplands in the Ohio River Valley in southern Illinois, roughly in the center of the Vacant Quarter. Analyses of artifacts and radiocarbon dating of burned wood taken from structures indicated that all three villages had been abandoned at about the same time, around 1450. That showed depopulation of the Vacant Quarter was not limited only to river valleys, Cobb and co-author Brian Butler wrote in a 2002 paper published in American Antiquity, but was “likely a widespread phenomenon that crosscut environmental zones.” Other studies have since supported that notion.

Researchers have also been tackling another challenge posed by Williams: figuring out exactly when the Vacant Quarter abandonment occurred, and whether it was “synchronic,” meaning it occurred roughly simultaneously everywhere. Williams initially proposed that abandonment had been synchronic and took place sometime between 1450 and 1550. But archaeologists have found that some sites, including Cahokia, were abandoned much earlier, perhaps by the mid-1300s. That suggested abandonment played out differently in different parts of the Vacant Quarter, with some settlements flickering out while others lingered on.

In a bid to construct a better chronology, about a decade

ago Anderson and Scott Meeks, who is now with the consulting firm Tennessee Valley Archaeological Research, undertook a Herculean task. They compiled 557 radiocarbon dates that archaeologists had obtained from charred wood and other artifacts found at 113 sites in the Vacant Quarter’s five main geographical regions. Taken together, the dates offered a rough guide to how much of the quarter had been occupied at any given time, and how populations had changed between 1200 and 1500. The analysis strongly suggested that abandonment had been synchronic, with “the most significant period of population decline” occurring between 1380 and 1420, they reported in a chapter of the 2013 book Soils, Climate and Society.

Meeks and Anderson also went a step further by examining one possible cause of abandonment: precipitation shifts that created food shortages. First they reconstructed how much water was likely available to farmers in the Southeastern U.S. between 1200 and 1500. The estimates were based on growth rings found in trees that grew in the region at the time: the width and density of the rings can indicate whether a year was wet or dry. Then, they calculated how much of one key staple—maize—the available water would have allowed farmers to grow, recognizing that both too much water (floods) and too little (droughts) can cause crop failure. Finally, the researchers calculated how shifting crop yields would have affected how much food communities could have kept in reserve to get them through hard times.

The researchers found that the farmers likely had adequate water to produce plentiful harvests in about three-quarters of the years between 1200 and 1500, and the Vacant Quarter populations appear to have expanded, or at least remained stable, during the wet years. But the region also experienced four extended droughts, with the shortest lasting eight years and the longest twenty-nine. The latter drought, which lasted from 1385 to 1413, appears to have been particularly devastating, with communities likely experiencing total crop failure during nearly half of that period. Vacant Quarter populations appear to have dropped severely due to the drought, and never really recovered. But it wasn’t clear that drought alone caused abandonment, Meeks and Anderson emphasized. The reality, they suggested, was likely far more complicated, involving an interplay of environmental stress and social factors.

Adesire to understand that complexity is driving the new study. “Climate change is sure looking like an important underlying driver of abandonment, but it also looks like not every community is responding in the same way at the same time,” said Cobb. And that makes sense, he added, because although the Vacant Quarter communities shared a “veneer of similarity,” they were different in a number of ways. Consequently, some communities might have responded to stress

Members of the Chickasaw Nation dig a trench at the Stark Farm site.

by changing their agricultural practices, for example, while others tried praying to their gods for rain, or simply declaring war on nearby communities and taking their land and food reserves.

To explore such differences, the research team is focusing on what happened prior to abandonment in two very distinct parts of the Vacant Quarter that are about 190 miles apart: the Middle Cumberland River Valley in Tennessee, on the quarter’s eastern edge, and the Upper Tombigbee River Valley in Mississippi, at its southern frontier. Archaeological evidence suggests the Middle Cumberland was a booming center of Mississippian culture, with a population that was relatively large for the Vacant Quarter. Residents built at least twenty-five multi-mound complexes as well as many smaller settlements. In contrast, populations in the Upper Tombigbee appear to have been sparser, and they built no known large multi-mound centers.

One major component of the project involves new field work at the Butler Mound near Columbus, in eastern Mississippi. It is just the third Late Mississippian site in the area to get intensive study. In 2016, researchers used remote sensing to identify a number of potential structures and other cultural features. They also collected and radiocarbon dated charred wood from near the top of the mound, and from one dwelling. “We can’t yet tell when mound construction began, but the preliminary radiocarbon dates suggest that construction was continuing into the late 1400s,” said Boudreaux, who is partnering with researchers and university students from the Chickasaw Nation to examine the site. If those dates hold up, he said, “we could be looking at one of the Vacant Quarter’s last occupied mounds.” The researchers will be comparing what they learn at the Butler Mound to data gathered at the two other, already documented, Mississippian sites in the region.

In Tennessee’s Middle Cumberland Valley, the researchers won’t be doing much digging. Instead, they will focus on analyzing the existing museum collections of ceramics and other artifacts that archaeologists have collected at seven Mississippian sites. One goal is to assemble a large new set of radiocarbon dates that will allow them to better understand when the Vacant Quarter sites were abandoned. And here, said Krus, is where the deceased cleric Thomas Bayes is lending a hand. His key concept, which has been realized thanks to the advent of modern computers, is that scientists can use their expert knowledge to improve calculations of probability. Bayes-inspired tools are now used routinely by political analysts, gamblers, and financiers to construct sophisticated virtual worlds, in which they run millions of simulations of elections, sporting events, and investment decisions. These simulations, which are informed by assumptions that the experts feed into the models, have proven adept at identifying the most probable outcomes.

In the Vacant Quarter study, the archaeologists are using Bayesian simulations for purposes such as determining how many samples of wood and other materials they will need to radiocarbon date in order to calculate highly-accurate occupation spans for the ten sites they’re investigating. Such finegrained information is key to understanding the chronology of abandonment, they noted. Krus concluded they will need to date 180 new samples (in addition to ninety-four already in hand), most of which will come from museum collections. The Bayesian tools “are a big help in helping decide how to maximize our sampling time and effort… to get the most robust conclusions,” Krus said. The simulations also help save money, since dating samples is expensive.

The team has also started reviewing published data on plant and animal remains found at their sites, in order to learn more about past local climates and what people were eating. And they are looking for evidence of social strife, such as the construction of palisades or other defenses against attacks, that might have set the stage for migrations. The researchers also plan to analyze the design and make-up of pottery found at sites, to see if ceramics were flowing between these settlements—a possible sign of population movements. Such studies could also shed light on where people went after they abandoned the Vacant Quarter. The ceramic studies, for example, could help confirm a suspicion that the Vacant Quarter residents living in the Upper Tombigbee River area migrated a few dozen miles west, where they occupied Stark Farm and other sites.

Anderson, for one, sees the new study—with its use of Bayesian modeling, paleoclimate and agricultural data, and fine-grained approach to resolving a large-scale puzzle—as a model for future investigations of other ancient abandoned homelands. Archaeologists have already identified several other regions in Eastern North America that appear to have experienced mass out-migrations, he noted. “We’re coming to understand that the prehistoric political landscape… was shifting [and] chaotic, with people abandoning some regions even as dense populations grew or stayed on in others,” he said. “So, I have no doubt we are going to recognize many, many more Vacant Quarters in the years to come.” And archaeologists, he suggested, need to be ready to explore the void.

DAVID MALAKOFF is a deputy news editor at Science and a frequent contributor to American Archaeology.