In 1850, Increase A. Lapham, an author, scientist, and naturalist, surveyed the site on behalf of the Smithsonian Institution, which was surveying ancient mounds. He described the outer stockade as being " long at the north end, long on the west side and on the south side; making a total length of wall of . The ridge or wall is about , and from to ) in height". It had at least 33 square bastions at regular intervals along its length, similar in form and placement to some European fortifications, in order to allow defensive warriors to cover that area by shooting arrows. In addition, others were built along the secondary walls. Rather than having a gate to protect the entrance, the builders constructed the entrance so that it was camouflaged from direct view and blended in with the wall on either side.