Native American tribes in Ohio and Illinois who, from c.1000 bc, erected richly furnished circular burial mounds, resembling the European barrows in shape and function. In the Mississippi basin some centuries later (c.700 ad), larger and more complex mounds, presumably for ceremonial gatherings, were raised to support temples. Though most were rectangular, and frequently built in large groups as at Cahokia in Illinois, there are more bizarre ones, such as the 400 m (1300 feet) long snake mound in Adams County, Ohio. These may have been influenced from Mexico.