The following is extracted from lecture 23 of Professor John R. Hale’s Exploring the Roots of Religion, course number 3650, The Great Courses:

On the banks of the Mississippi, in Western Illinois, stands the largest earth structure for its time in the New World. In the 11th century, this mound was the centre of the largest urban complex within the frontiers of what is now today the United States, and this urban conglomeration was a larger urban centre than London then was. What was this mound for? Well, it was a big mound: it rises 100 feet above the ground. This mound at Cahokia was a temple mound. There was a temple on its Northern side, which was 100 foot long, and probably had a thatched roof.

It seems to archaeologists and anthropologists today, that this city was held together by religious faith. It was a great city, marked by mounds. The city is orientated around a central plaza (several times larger than St. Peter’s Plaza in Rome). There were communities of people who manufactured sacred objects, the raw materials for which were brought in from elsewhere: obsidian, from Yellowstone Park, copper from Lake Superior, marine shells from the Gulf of Mexico, mica from the Smokey Mountains; and other semi-precious stones were imported from elsewhere. They manufactured and exported pottery, woven cloths, and agricultural tools like a hoe made of white flint; and arrow-heads made by flint-knapping.

There were great feasts held on magnificent scales. Trenches have been discovered with the remains of thousands of deer, soups of pumpkin and gourd, nuts, berries, and millions of smoked tobacco seeds. Tobacco was smoked as a sacred pastime.

This was a large population, of approximately estimated to be 20,000 people, who could be mobilised for giant construction projects: such as building sacred structures, and moving large amounts of earth. The population might have been centred religiously around building mounds.

Professor Hale concludes that,

Not only do we have an extraordinarily rich ceremonial life here, not only is the whole community involved in these rich ceremonial feasts, but that the ruler represented the sun, that the deity worshipped in that upper temple, on top of that pyramid — the great mound — was indeed the sun; and that what we are seeing here at Cahokia, are people who have invested their lives in agriculture, who depend on the sun, more than any other natural force for their success and the preservation of their community; who have built their religion around it: a religion that after Cahokia was abandoned at about 1400, spread then among other centres and remote tribes, who carried down into the historic period recollections and a memory of the Native American first great solar faith.