Where in the Americas is the richest concentration of mound buildings?

The richest concentration of mound buildings in the Americas is found in the southeastern United States, particularly in regions like the Mississippi River Valley. Notable sites include Cahokia, located near present-day St. Louis, Missouri, which was the largest pre-Columbian city in North America and featured numerous large earthen mounds. These mound complexes served various purposes, including ceremonial, burial, and residential functions, reflecting the advanced societal structures of the indigenous cultures that built them.