Between the 9th and 15th centuries, the local Indigenous people created a religious and political center, culturally linked to the Southeastern Ceremonial Complex identified by anthropologists as the Mississippian Ideological Interaction Sphere (MIIS).

In the 1930s during the Great Depression, treasure hunters bought the rights to tunnel into Craig Mound—the second-largest mound on the site—to mine it for artifacts.

Without concern for scientific research, they exposed a hollow burial chamber inside the mound, a unique feature containing some of the most extraordinary pre-Columbian artifacts ever found in the United States.

The artifacts included works of fragile, perishable materials: textiles and feathers that had been uniquely preserved in the conditions of the closed chamber.

The largest Mississippian settlement was Cahokia, the capital of a major chiefdom that built a six-mile-square city east of the Mississippi River that now is St. Louis, Missouri, in present-day southern Illinois.

Archeological studies have revealed that Mississippian culture extended from the Great Lakes to the Gulf Coast, along the Ohio River, and into both the lowland and mountain areas of the Southeast.

The mounds were arranged around large, constructed flat plazas believed to be used for ceremonial community gathering and ritual games.

The conditions in this hollow space were so favorable that objects made of perishable materials such as basketry, woven fabric of plant and animal fibers, lace, fur, and feathers were preserved inside it.

Also found inside were several examples of Mississippian stone statuary made from Missouri flint clay and Mill Creek chert bifaces, all thought to have originally come from the Cahokia site in Illinois.

The "Great Mortuary", as archaeologists called this hollow chamber, appears to have begun as a burial structure for Spiro's rulers.

Some scholars believe that minerals percolating through the mound hardened the log walls of the chamber, making them resistant to decay and shielding the perishable artifacts inside from direct contact with the earth.

These materials included colored flint from New Mexico, copper from the Great Lakes, conch (or lightning whelk) shells from the Gulf Coast, and mica from the Carolinas.

[11] Using these valued materials, Mississippian artists created exquisite works of art reflecting their cultural identity and their complex spiritual beliefs.

The conch shells were fashioned into gorgets and drinking cups engraved with intricate designs representing costumed humans, real and mythical animals, and geometric motifs, all of which had profound symbolic significance.

Later, archaeologists recognized that the ritual artifacts at Spiro were similar to comparable objects excavated at other powerful Mississippian towns that also participated in the Southeastern Ceremonial Complex.

In economic terms, Spiro seems to have been a gateway town that funneled valuable resources from the Great Plains and other western regions to the main Mississippian ceremonial centers farther east.

Spiro and other Mississippian towns clearly looked to the great city of Cahokia, in what now is southern Illinois, as a cultural model to be emulated.

Located about 400 miles northeast of Spiro near the confluence of the Mississippi and Missouri Rivers, Cahokia was the largest and most impressive of all the Mississippian towns.

The new scheme divides the SECC into five periods, or horizons, each defined by the appearance of new ritual objects and cultural motifs connected with new developments in politics and long-distance trade.

Anthropologists have tried in recent years to interpret the meaning of the ritual artifacts and artistic imagery found at Spiro and other Mississippian sites.

Another Spiro icon is the "Great Serpent", a being said to inhabit the Under World, the spiritual domain on the opposite side of the Mississippian universe.

Similar beings were the subject of myth in historic times among the Micmac, Huron, Kickapoo, Cherokee, Muscogee Creek, Caddo, and other Native American tribes, representing at least three major language families.

Often, the cedar tree, or the striped-center-pole, is found on engraved conch shell gorgets, with human or animal figures positioned on either side.

This suggests that the Spiro people may have practiced a version of the Black Drink Ceremony, a purification ritual that was also performed in historic times by their descendants—the Southeastern tribes.

[18] When the Spanish conquistador Hernando de Soto led a military expedition into what is now the southeastern United States in the 1540s, he encountered Native American groups including the Tula people, who lived near the Arkansas River.

Scholars have determined that Battle Mound, lying along the Great Bend of the Red River in southwest Arkansas, was a larger site than Spiro.