The Caddoan Mississippian culture appears to have emerged from earlier groups of Woodland period groups, the Fourche Maline and Mossy Grove culture peoples who were living in the area around 200 BC to 800 AD. By 800 AD early Caddoan society had begun to coalesce into one of the earlier Mississippian cultures. Some villages began to gain prominence as ritual centers, with elite residences and platform mound constructions. The mounds were arranged around open plazas, which were kept swept clean and used for ceremonial occasions. The Caddoan homeland was on the geographical and cultural edge of the Mississippian world and had similarities to both Mississippian Culture and Plains Traditions. The Caddoan communities were not as large as other eastern and southern Mississippian communities, they were not fortified, and they did not establish large, complex chiefdoms; with the possible exception of the Spiro Mounds on the Arkansas River. As complex religious and social ideas developed, some people and family lineages gained prominence over others. This hierarchical structure is marked in the archaeological record by the appearance of large tombs with exotic grave offerings of obvious symbols of authority and prestige, such as those found in the "Great Mortuary" at Spiro.