The largest pre-Columbian settlement in the New World north of Mexico, Cahokia once had about 120 mounds, built for various purposes by the inhabitants of the area. One of these mounds is Monks Mound which, at nearly 100 feet tall, is the largest earthwork in North America from prehistoric times.
Near present day St. Louis, Cahokia was a center of culture and religion for possibly up to 20,000 people of the Mississippian cultural tradition. At it's height in roughly the year AD 1250, Cahokia was bigger than London. It was first settled around AD 600 and mounds were built starting about 300 years later. The settlement continued until perhaps as late as the early 15th century, when it was abandoned for unknown reasons. Many theories have been proposed for the abandonment , including invasion and warfare, as well as lack of game animals and deforestation as a result of erosion.
Within the ceremonial complex there was a wooden monument built to mark the equinox and solstice, in much the same way that Stonehenge in England does. The remnants of the wood poles were discovered by archaeologists and a replica has now been built.
The area now encompassing Cahokia Mounds State Historic Site in Collinsville, Illinois has a long and sordid history. In addition to it's status as a center of trade and culture, it also existed as a large ceremonial and ritual complex. One mound in particular, Mound 72, shows evidence of hundreds of sacrificial burials. Contained within the mound are 4 male skeletons buried together, all missing their hands and skulls.
Also within this mound, skeletons in a mass grave were found with their fingers extended in to the sand surrounding them, suggesting to archaeologists that the people were alive when they were buried and were trying to claw their way through the dead bodies surrounding them. The skeletons in this grave were all of women in their early 20s, which further suggests that these individuals were not opponents in war but were sacrificial victims.
Cahokia Mounds State Historic Site became a UNESCO World Heritage Site in 1982.