E. H. Davis, Ancient Monuments of the Mississippi Valley
“ South of the bluff the walls are continued of the same height and thickness, until they reach the angles of the wall fronting the south, which wall also extends from the bank of one river to the other, and has a gateway nearly opposite to that in the northern wall. At the points a a, it is supposed by many who have examined this work, there were formerly excavated passages leading to each branch of Duck river, with steps cut in the rock. There does not, however, appear to be sufficient evidence to sustain this conclusion. The ascent or descent is not very difficult ”
