This is the site of Big Mound, the largest of the monumental earth mounds that people of the Mississippian civilization built in St. Louis about a thousand years ago. St. Louis at the time was a satellite city, maybe a sort of suburb, to the main center across the river at Cahokia Mounds. A third large group stood in between, in East St. Louis.
The St. Louis Mound Group contained at least 25 mounds. They were located just to the north of today's downtown, roughly between Cass Ave and Laclede's Landing. The mounds encircled a central plaza, as at Cahokia; but unlike Cahokia, the largest mound was not on the plaza but was set about 600 meters to the north. The French called it the Grange de Terre , and the Americans just called it Big Mound. It was measured at 319 feet long, 158 feet wide, and 34 feet high. It had an oval shape and a ridge top.
Based on the size, shape, and position of Big Mound - as well as eyewitness accounts of artifacts that were found in it - archaeologists mostly agree that it was built for human burials. Like other ridgetop mounds around Cahokia, Big Mound probably contained the remains of several high-status people. Most likely, builders first made a huge platform of earth and ceremonially laid the remains on it. They then covered the bodies with a "roof" of earth to give the mound its distinct ridgetop shape. Such mounds were rare and unique to the greater Cahokia/St. Louis area. Probably they were among the most sacred sites in the region.
In the 19th century, people called St. Louis "Mound City" because of this construction and the others nearby. But as the modern city grew, the ruins of the ancient one were destroyed one by one. Big Mound came last, being taken down for fill dirt in 1869. A very small monument marks the location, overshadowed by the new I-70 bridge.
Note: The little monument was taken down before November 10 and the original cache disappeared with it. Many thanks to Mean Gene and roelsch for replacing the container!