It was settled around the 7th century, gradually evolving into a great urban center, populated more densely than London of the same time. For decades thousands of workers had shifted more than 55 million cubic feet of earth, building a great network of mounds and ceremonial plazas.
Over 120 mounds spread through the busy, bubbling, noisy city, with its crowded neighborhoods, smelly marketplaces and the multitude of different-size pyramids, some ridge-top for the burial purposes, some flat, platform-top for the ceremonial ones. The deceased rulers would be buried there, placed in a bed of the thousands marine shells, arranged sacredly in a form of this or that deity, with a treasure of many valuables – arrowheads, copper jewelry and, sometimes, a pile of sacrificial victims.
Wooden stockade, fortified with watchtowers, enclosed the important, ceremonial center of the city, separating the nobility from the lower classes. The neighborhood of the elite has to be kept quiet, cherished and protected. The royal Great Mound, ten storey tall, spacious and terraced, hosted main temples and the large dwelling of the ruler, who was tracing his dynasty to the Sun God himself. In order to protect the purity of the bloodline, the throne would always pass from the Ruler to his nephew, the son of his blood sister. No mortal noblewoman, married to the descendant of the Sun God, chaste as she might appear, could be trusted with delivering a pure blood next ruler.
Artificially made, adjacent Grand Plaza of almost 40 acres served for ceremonies and games, along with the smaller plazas, encircling the Great Mound. And, of course, astronomical observations were have to be conducted, in order to appease the gods properly. To the west of the Great Mound, Woodhenge – a circle of poles – served to track the movements of the major stars, marking mainly the solstices and the equinoxes.
Cahokia declined toward the 14th century. It may have begun with the climate changes that have, probably, affected the whole region, up to the west coast (approximately around this time, Anasazi had also abandoned their Great Houses in Arizona and Colorado canyons). It may be that the Cahokians themselves helped to affect the climate, deforesting the area unmercifully. Or maybe in such a large, densely populated urban center (up to 40,000 residents at its height) the diseases began to spread, thinning the population out.
Whatever the reason, Cahokia was no more, long before the first contact with the Europeans was made.