Archaeology professors have discovered in Illinois what they said appears to be a coppersmiths' workshop from the American Stone Age.

Ancient Mississippian-era hammered-copper decorations, including headdress ornaments, jewelry and clothing embellishments, have been unearthed near the Cahokia Mounds State Historic Site in Collinsville, the Belleville News-Democrat reported Tuesday.

The site was the location of Cahokia, a large, prehistoric city of perhaps 20,000 inhabitants, the News-Democrat said.

A self-taught archaeologist, Greg Perino, who died in 2005 at age 91, originally found the workshop in the 1950s. Perino had mapped the area of the site, but his mapping was crude and made it difficult to locate the site, the newspaper said.