A publication of the Archaeological Institute of America
Mapping a prehistoric American metropolis
The trio of massive earthen mounds rising from the banks of north Georgia's winding Etowah River are monuments of a great prehistoric North American culture. The tallest, which stands higher than a six-story building above the surrounding grassy plain, is one of the largest structures ever built by the Mississippian societies that dominated much of the land from eastern Oklahoma to northern Florida from about A.D. 1000 to 1500. At Etowah, as at other Mississippian sites, the mounds were used for a variety of purposes: platforms for buildings, stages for ceremonial events, and cemeteries for the communities' elite.
Courtesy Adam KingWith the largest of Etowah's mounds in the background, archaeologists prepare to survey a section of the site with ground-penetrating radar. From left, Emman Spain of the Muscogee Nation's cultural preservation office; Chester P. Walker of Archaeo-Geophysical Associates, LLC; and Dan Bigman, a University of Georgia graduate student. (Courtesy Mike Toner)
Mindful that many decades of archaeological investigations had preceded him, University of South Carolina archaeologist Adam King was uncertain what, if anything, he might discover when he and a multi-institutional team of investigators decided in 2005 to see if remote sensing and geophysical tests might reveal something a century of traditional archaeology had missed.
Using a suite of equipment to measure underground magnetism, density, and electrical properties, King's team has mapped--in just three field seasons--the subsurface remains of the prehistoric town that once covered much of the 50-acre plain surrounding Etowah's imposing mounds. The results have broadened archaeologists' understanding of the site in a relatively short period of time. And it was done without turning a single shovelful of earth, which eased the concerns of Native American communities that have been resistant to more overt disturbance of what, to them, is a sacred place.
Instead of digging the hundreds of thousands of test pits that traditional archaeology would have required to fully assess what lay beneath the surface of such a sprawling site, King's team used portable sensors--some handheld, some dragged over the ground on wheeled "sleds"--to map subtle variations, or anomalies, in the soil. The readings, made at intervals of little more than four inches, were analyzed, digitized, and turned into maps of ancient Etowah's buried landscape.
A shell gorget (pendant), left, and a copper plate, right, both found at Etowah, date to the 13th century. They depict the Birdman, a heroic figure important to ancient Mississippian peoples. These pieces would have been worn as chiefly regalia during important religious ceremonies. (Courtesy David H. Dye; Courtesy Smithsonian Institution)
"Since we started, we have identified a total of 140 buildings. They range from dense clusters of houses around small plazas to some very large buildings, including one structure that's nearly 100 feet on a side," says King. "Archaeologists have been digging at Etowah for 120 years, but despite its fame, a great deal of the site was just never explored," he says. "We now have a wealth of new archaeological information regarding the site's history, including [evidence of] old excavations, portions of the surrounding palisade, and many of its structural remains." The new data are revealing critical details about Etowah's social structure and chronology. "It is clearly a much more complex place than we imagined," says King.
Since the work of the Smithsonian Institution's John P. Rogan in 1883, excavations have unearthed thousands of artifacts, including elaborately carved marine shell gorgets (pendants worn as personal adornment), feathered headdresses, sleek ceremonial axes, pipes, and exquisitely crafted copper plates that were used to decorate chiefly attire. A pair of three-foot-high painted marble effigies of a seated man and woman--unearthed by former Georgia state archaeologist Lewis Larson in the 1950s along with human remains from a wooden tomb--are among the most well-known finds. King says many other excavated objects may have been lost or misplaced by earlier investigators (and many of the findings were never published). So a lot of information about Etowah has been irretrievably lost. "The focus of early archaeology was to get stuff--important, exciting stuff," says King. "Everyone knew they were going to find stuff in the mounds, so that's where they dug."
Early archaeologists could not have imagined the 21st-century tools and technology that King's team has been using to map the features of Etowah's unseen cultural landscape.
"It used to be that the only way we could learn about the overall distribution of different kinds of structures was through broad excavation projects--and those required a lot of time and labor," says the team's co-investigator Chester P. Walker. His firm, Austin, Texas-based Archaeo-Geophysical Associates, LLC, has been providing most of the project's technological expertise. "But now, with remote-sensing technology and our growing ability to process the huge amounts of data we collect, we can find out a lot about an area in a very short time," he says.
"Ultimately, I think Etowah will be a benchmark for how far we can push this suite of remote-sensing techniques," says state archaeologist David Crass. "Remote-sensing hardware and post-processing software are advancing so fast that the capabilities are now far beyond what they were just 10 years ago. This means that we can now go back to sites like Etowah that have been previously investigated and glean a whole new set of useful data."
Mike Toner is a freelance writer and former science writer for The Atlanta Journal-Constitution.