SPIRO MOUNDS. One of Oklahoma's most important prehistoric American Indian sites, Spiro Mounds is located in Le Flore County on the southern bank of the Arkansas River about fifteen miles from Fort Smith, Arkansas. The Spiro Mounds site grew from a small farming village to one of the most important centers in what later became the United States. Between A.D. 850 and 1450 twelve mounds, ceremonial areas, and a support city were eventually created for the Caddoan-speaking leadership who participat