The mounds were once ceremonial pyres, although it's unclear if they were used to incinerate humans or animals. According to recent findings published in the American Journal of Science, two six-meter (20-foot) high mounds on the campus of Louisiana State University (LSU) are the oldest man-made structures yet found in North America. The construction of the mounds began some … [Read more...] about The Oldest Known Human-Made Structures in North America are Ceremonial Mounds, Which Date Back 11,000 Years