Mounds were used for burial, to support residential and religious structures, to represent a shared cosmology, and to unite and demarcate community. Common forms include conical mounds, ridge-top mounds, platform mounds, and animal effigy mounds, but there are many variations. Mound building in the USA is believed to date back to at least 3400 BC in the Southeast (see Watson Brake). The Adena and the Mississippian cultures are principally known for their mounds, as is the Hopewell tradition. The largest mound site north of Mexico is Cahokia Mounds, a vast World Heritage Site located just east of St. Louis, Missouri.