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North American Plains Indians of the Caddoan linguistic family. The cultural roots of Caddoan-speaking peoples lay in the prehistoric mound-building societies of the lower Mississippi River valley. The Arikara were culturally related to the Pawnee, from whom they broke away and moved gradually northward, becoming the northernmost Caddoan tribe. Before American colonization of the Plains, the Arikara lived along the Missouri River between the Cannonball and Cheyenne rivers in what are now North and South Dakota.