The Mound Builders were a Pre-Columbian people whose history spanned at least two thousand years, starting shortly before the Adena culture, including the Hopewell culture, and lasting through the fall of the Mississipian civilizations, including the culture now known as the Cahokians.

Their namesake cultural trait, of course, was the building of earthworks; dirt structures often resembling flat-topped pyramids, cones, or other similar shapes, initially used for burial but eventually for other ceremonial functions and perhaps more.

The most exceptional examples of these would be Monk's Mound, a 100 foot tall structure reminiscent of Mesoamerican pyramids, and Serpent Mound, which is only 5 feet tall and 20 wide, but over 1330 feet long, in the shape of, as the name implies, a serpent.

The mound builders tended to form static civilizations, with villages, cities, government, et cetera, somewhat reminiscent of Mesoamerican civilizations like the Aztecs, Incas, and Mayans, except on a smaller scale.