The Mississippian culture was a Native American civilization that flourished in what is now the Midwestern, Eastern, and Southeastern United States from approximately 800 CE to 1600 CE, varying regionally. It was known for building large, earthen platform mounds, and often other shaped mounds as well. It was composed of a series of urban settlements and satellite villages linked together by loose trading networks. The largest city was Cahokia, believed to be a major religious center located in what is present-day southern Illinois. The Mississippian way of life began to develop in the Mississippi River Valley (for which it is named). Cultures in the tributary Tennessee River Valley may have also begun to develop Mississippian characteristics at this point. Almost all dated Mississippian sites predate 1539–1540 (when Hernando de Soto explored the area), with notable exceptions being Natchez communities. These maintained Mississippian cultural practices into the 18th century. Cultural traits A number of cultural traits are recognized as being characteristic of the Mississippians. Although not all Mississippian peoples practiced all of the following activities, they were distinct from their ancestors in the adoption of some or all of these traits. The construction of large, truncated earthwork pyramid mounds, or platform mounds. Such mounds were usually square, rectangular, or occasionally circular. Structures (domestic houses, temples, burial buildings, or other) were usually constructed atop such mounds. Maize-based agriculture. In most places, the development of Mississippian culture coincided with the adoption of comparatively large-scale, intensive maize agriculture, which supported larger populations and craft specialization. Shell-tempered pottery. The adoption and use of riverine (or more rarely marine) shells as tempering agents in ceramics. Widespread trade networks extending as far west as the Rocky Mountains, north to the Great Lakes, south to the Gulf of Mexico, and east to the Atlantic Ocean. The development of the chiefdom or complex chiefdom level of social complexity. The development of institutionalized social inequality. A centralization of control of combined political and religious power in the hands of few or one. The beginnings of a settlement hierarchy, in which one major center (with mounds) has clear influence or control over a number of lesser communities, which may or may not possess a smaller number of mounds. The adoption of the paraphernalia of the Southeastern Ceremonial Complex (SECC), also called the Southern Cult. This is the belief system of the Mississippians as we know it. SECC items are found in