Finding forgotten Indigenous landscapes with electromagnetic technology

Although monumental earthworks can be found from southern Canada to Florida and from Wisconsin to Louisiana, Ohio has the largest known collection of these structures in the United States—despite the fact that Ohio has no federally recognized Native American tribes. Their creators have been lumped together under a vague term, “Hopewell Culture,” named after the family on whose farmland one of the first mounds to be studied was found. Cultural activities associated with the Hopewell are thought to have ended in the Ohio region around 450 to 400 BCE. Tribes such as the Eastern Shawnee, the Miami Nation, and the Shawnee—who, historians believe, are the mound builders’ most likely modern descendants—were violently displaced by the European genocide of the continent’s native population and now live on reservation lands in Oklahoma. 

Glenna Wallace, chief of the Eastern Shawnee Tribe, is one of those descendants. When we spoke, Wallace was on her way to Washington, DC, to meet President Joe Biden for the White House Tribal Nations Summit. These annual events were first convened in 2009 by President Barack Obama but were discontinued during the Trump administration. Wallace had only recently returned from southern Ohio, where she had been visiting sites associated with her tribe’s ancient roots. “The Native American voice has not been very strong in Ohio. The things that our people accomplished there have not necessarily received the best protection that should be possible,” she told me. “The people have been forced to leave, and our mounds have not been taken care of.” 

Burks and I had driven roughly 70 miles southeast from Columbus, along meandering highways lined with creeks and roadkill, to reach a small family farm in the foothills of the Appalachian Mountains. The trees around us were crisp with autumn leaves. A herd of cattle wandered past, their muscular backs framed against rolling hills in the distance. As Burks completed the 20-minute process of assembling his magnetometer—once complete, it would form a pushcart nearly seven feet wide, weighing roughly 30 pounds—he emphasized that the vast majority of the artificial hills and mounds he spends his time looking for were physically dismantled long ago. In only a few cases were those earthworks first excavated or studied; instead, they were simply plowed over; bulldozed to build roads, homes, and shopping malls; or, in one infamous case, incorporated into the landscaping of a local golf course. 

Archaeologists believe that these earthworks functioned as religious gathering places, tombs for culturally important clans, and annual calendars, perhaps all at the same time.  

Until recently, it seemed as if much of the continent’s pre-European archaeological heritage had been carelessly wiped out, uprooted, and lost for good. “People see plowing and think it’s completely destroyed the archaeological record here,” Burks said, “but it’s still there.” Traces remain: electromagnetic remnants in the soil that can be detected using specialty surveying equipment. Here, in this very pasture, he added, were once at least three circular enclosures. Our goal that morning was to find them. 

Magnetometry—Burks’s specialty—is capable of registering even tiny variations in the strength and orientation of magnetic fields. When pushed across the landscape, a magnetometer can detect where those fields in the soil below have changed, potentially indicating the presence of an object or structure such as old walls, metallic implements, or filled-in pits that might be graves. Magnetometry is also extremely good at finding hearths or campfires, whose heat can permanently alter the magnetism of the soil, leaving behind a clearly detectable signature. This means that even apparently empty pastures—or, of course, community golf courses and suburban backyards—can still contain magnetic evidence of ancient settlements, invisible to the naked eye. 

Given such a context, knowing where to begin scanning is the first hurdle. Luckily for archaeologists and tribal historians alike, Ephraim George Squier and Edwin Hamilton Davis—a two-man team working in the middle of the 19th century—mapped as many earthworks as they could find, motivated to learn more about these artificial landforms before they were destroyed or permanently forgotten. Explaining their project’s rationale, the authors wrote that the earthworks had received only passing descriptions in other travelers’ logs and, they thought, “should be more carefully and minutely, and above all, more systematically investigated.” Doing so, they hoped, was their way of “reflecting any certain light upon the grand archaeological questions connected with the primitive history of the American Continent.”