Just ran across this today. Never heard of it before. From the Wiki page:
Poverty Point comprises several earthworks and mounds, built between 1650 and 700 BCduring the Archaic period in North America, by a group of Native Americans of the Poverty Point culture. The culture extended 100 miles (160 km) across the Mississippi Delta. The original purposes of Poverty Point have not been determined by archaeologists, although they have proposed various possibilities, including that it was a settlement, a trading center, and/or a ceremonial religious complex.
The 910-acre (1.42 sq mi; 3.68 km2) site, which has been described as “the largest and most complex Late Archaic earthwork occupation and ceremonial site yet found in North America“ is a registered National Monument. The monument was brought to the attention of archaeologists in the early 20th century, when it was given the name of Poverty Point after a nearby plantation.