Double Ditch State Historic Site in North Dakota: Kvamme uses colored lines to illustrate the fortification ditches shown through electrical resistivity (the blue field). Red and green lines indicate the newly discovered ditches. Brown areas indicate midden mounds.

This electrical resistivity map shows three lines of ditches. 15th century bastions can be seen on the right, along the outermost ditch.

FAYETTEVILLE, Ark. - Using geophysical technologies to image features buried beneath the soil, a University of Arkansas archeologist has mapped a Native American settlement that, by its unusual size and content, could rewrite our understanding of Great Plains prehistory, offering new insight into early civilization and warfare in North America.

For two weeks this past summer, Ken Kvamme, associate professor of anthropology, applied ground penetrating radar, electrical resistivity and magnetometry readings to the Double Ditch State Historic Site in North Dakota - long believed to be the location of an 18th century Mandan village.

What Kvamme found beneath the soil not only pushed the date of the village back three centuries. It extended the boundaries of the site to reveal one of the largest native settlements west of the Mississippi, and it suggested forms of defensive warfare never before associated with Great Plains tribes. Kvamme presents his findings today at the Plains Anthropological Society meeting in Oklahoma City.

"Double Ditch is a fairly shallow site, so close to the surface that you can actually see some of the house depressions where the Mandan earthlodges sat and the line of the two fortification ditches that surrounded the village," Kvamme said. "But what we found with the geophysical instruments were two completely hidden fortification ditches way out beyond the original two. It nearly doubles the size of the village."

Built as a defensive measure against invaders, the fortification ditches originally would have been 1-2.5 meters deep and nearly two meters wide with a palisade constructed on the inside edge. According to Kvamme, the newly-discovered ditches enclose an area of approximately 7.5 hectares, representing a substantial engineering feat.

"We know of ongoing hostility between the Mandan and the Sioux or Dakota in historic times, but to consider the tremendous amount of energy it would have taken to dig these fortifications around such a large area - it clearly tells us these people lived in fear during the prehistoric era," he said.

But what Kvamme considers most curious about the new fortification ditches - and what he expects to cause a stir among his colleagues - is not just the area they enclose. Rather, it’s the placement of the ditches in relation to various midden mounds located along the periphery of the site. His geophysical maps reveal that the ditches follow the line of the middens around the village, suggesting that these earth-covered mounds of refuse may have played a role in the ancestral Mandans’ defensive tactics.

"The mounds could have been used as observation platforms, but the steep sides along the fortification ditch suggest that they may have served as something like ramparts," Kvamme explained. "Use of ramparts is totally unknown in Great Plains prehistory. They’re considered a European innovation in this region."

If Kvamme’s theory proves correct, the midden mounds at Double Ditch may constitute the first evidence of ramparts in Great Plains warfare - a significant innovation, considering that the form of those middens suggest they pre-date European contact with the New World.

With the help of archeologist Stanley Ahler of the Paleo Cultural Research Group, Kvamme has collected significant evidence that the village at Double Ditch may date back as early as the 1400s. After Kvamme mapped the new fortification ditches with electrical resistivity and magnetometry, Ahler’s team excavated portions of the site. They found potsherds in the outermost ditches, characteristic of 15th century pottery.

Furthermore, in surveying a greater area of the site, Kvamme’s maps revealed bastions along the exterior ditch - a common defensive feature, employed by the prehistoric occupants of the 1400s. His readings also showed the outline of rectangular houses mixed among the circular earthlodges. It is believed that the ancestral Mandan typically built rectangular lodges in the 15th century, switching to the circular shape later in prehistory. Kvamme and Ahler intend to perform radiocarbon dating to provide a more exact time-frame for the village.

Considering the size of the site, the number of houses and food storage pits it contained and the chronology of the village, a new picture of Double Ditch has emerged as a major North American settlement. Although a detailed study has not yet been conducted, the site may have supported as many as 3,000 people, with a record of continuous occupation spanning three centuries, Kvamme conjectured.

"To say the least, it’s uncommon for a Plains tribe to be settled in one area for such a long time. Even before we found the outer ditches, Double Ditch was one of the biggest Great Plains villages we knew about," he said. "So what’s going on out there is a tremendous place. This should really be nominated as a World Heritage Site. It’s that significant."

Amidst all the speculation about the size of the village, its occupants and their enemies, Kvamme can state one thing for certain: "The site needs a new name. With at least four defensive ditches now discovered, Double Ditch is something of an understatement."

Kvamme has spent more than a decade promoting the use of geophysical technologies to complement and guide archeological fieldwork. For more information about his projects, visit his Web site at To learn more about geophysical technologies and their use in the United States, visit the North American Database of Archeological Geophysics at -- a site designed and maintained by Kvamme and originally funded by the National Park Service.




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