Were huge circular piles of shell dumped along the southeast U.S. coast 3–5,000 years ago built as freshwater reservoirs for local tribes? That’s what at least one archaeologist, William Marquardt of the Florida Museum of Natural History, and a hydrologist Douglas Middaugh think. They believe that during periodic droughts some 4,000 years ago, local tribes were forced to build big holding tanks to capture and maintain an adequate supply of drinking water. Marquardt suggests in a 2010 article in American Antiquity that these “rings” built from oyster shell were used to capture rain and ground water.
Other archaeologists, including Dr. Mike Russo of the Southeast Archeological Center (SEAC) are not so sure. The standard view holds that people lived along the inside edge of the rings and threw the shell from their many meals behind them, which over decades—and sometimes centuries—formed the enormous ring structures that still stand today. Because the ring plazas hold evidence of houses, hearths, burials, and food storage, it seemed unlikely to us that rings were used to hold water. But Dr. Russo also suspected the freshwater reservoir idea was way off simply because loose piles of shell and the sand upon which shell rings were built cannot hold water. Put simply, shell and sand structures leak.
To test this idea, Dr. Russo and his colleagues at SEAC built a large ring of shell to see if it could hold water. The experiment and its results can be seen here:
Shell rings were huge structures even by today’s standards (some are larger than two football fields across and up to 20 feet high). At the time they were built they the largest structures in North America that would not be matched in size for another 3,000 years when the large stone temples in Central America began to appear. Unlike stone pyramids, shell rings were not built as a single event, public works construction projects. Rather they were built gradually over time.
But like all prehistoric living places, rings were also places of celebration, ritual and feasting. Much of the shell in the rings resulted from feasting at these celebrations held in the central plaza, which functioned much like a football field. To have a clear field for their rituals, plazas were kept scrupulously clean from the shell refuse that made the ring. Some of the rituals undoubtedly involved games, some marriages or other alliances, and we even have direct evidence of human burials in some plazas. But for the most part, we still don’t have evidence of what specific celebrations and rituals were performed at the rings.
For a more detailed account of the results, Dr. Russo’s and colleagues’ formal essay on the shell ring experiment can be found here: