High on the bluffs overlooking the east bank of the Missouri River, Double Ditch was the largest of the Mandan towns from the Heart River archaeological period, and was occupied from around 1675 to 1780. The visible archaeological features consist of two concentric ditches, mounds from two to ten feet high, collapsed earthlodges marked by circular sunken depressions, and smaller depressions marking the location of storage pits. As evidence of architectural aspiration, the two concentric ditches were originally dry moats up to nine feet deep and twenty feet across, and were probably associated with a log palisade that formed a defensive perimeter around the town. It appears that the outer ditch, about eight hundred feet in diameter, was created first, and that the town contracted and created a tighter organization, which was then enclosed in a five-hundred-foot oval ditch. The smallpox epidemic of 1781 resulted in the final abandonment of the site.