Spiro Mounds in eastern Oklahoma was a major western center of the Mississippian world, built by people of the Arkansas Valley Caddoan culture. Although the site saw human activity for at least 8,000 years, its main development came from about 800 to 1450 CE, when it became an important religious, political, ceremonial, and mortuary center within the Southeastern Ceremonial Complex. Its 12 earthen mounds and central plaza formed a planned civic and ritual landscape, while Craig Mound held elite burials and remarkably preserved objects from a far-reaching exchange network. Looting in the 1930s damaged the site, but later archaeological work and preservation protected its importance.