Even more populous than the Black Bottom was the American Bottom along the Mississippi River, extending twenty-five miles with a maximum width of eleven miles. The center of the American Bottom was the Cahokia site, covering more than five square miles and containing over a hundred mounds. Cahokia may have supported a population of over ten thousand, in addition to tens of thousands who lived less than a day’s walk from the site. Flat-topped mounds may have supported elite residences or public buildings, and conical mounds were used for burials. The largest of the mounds, named Monks Mound after Trappist monks built a monastery on it, is 100 feet tall and covers more than 18 acres, making it the largest man-made mound in the United States and larger at its base than both the Pyramid of the Sun in Mexico and the Great Pyramid of Giza in Egypt. It was built from soil carried in baskets. Cahokia and other major sites demonstrate that most levels of Mississippian settlements were arranged according to a hierarchy, with smaller sites surrounding larger sites, from hamlet-farmstead clusters up to major centers.