Ancient Monuments (more familiarly known as "Squire and Davis") is the undisputed primary reference source on Indian mounds in the eastern US till the mid-1800s. While there were a few others (such as Caleb Atwater's book), Squire and Davis offers the grandest illustrations of what remained of the unbelievable civilizations that inhabited this continent. Even as they published in 1848, hundreds of mounds were being plowed into oblivion; so few are still extant that theirs is the only guide to what was lost. The text is enjoyable on many levels, and can be forgiven for any lapses of scientific accuracy. They trekked over Ohio at a time when we weren't even sure who made the mounds, so everything they recorded is gold. The engineering prowess, the sheer magnificence and scale of some of the works, is astounding.