Monks Mound - Construction and Abandonment

Construction and Abandonment

Construction of Monks Mound by the Mississippian culture began about 900–950 CE, on a site which had already been occupied by buildings. The original concept seems to have been a much smaller mound, now buried deep within the northern end of the present structure. At the northern end of the summit plateau, as finally completed around 1100 CE, is an area raised slightly higher still, on which was placed a building over 100 ft (30 m) long, the largest in the entire Cahokia Mounds urban zone. Deep excavations in 2007 confirmed findings from earlier test borings, that several types of earth and clay from different sources had been used successively. Study of various sites suggests that the stability of the mound was improved by the incorporation of bulwarks, some made of clay, others of sods from the Mississippi flood-plain, which permitted steeper slopes than the use of earth alone.

The most recent section of the mound, added some time before 1200 CE, is the lower terrace at the south end, which was added after the northern end had reached its full height. It may partly have been intended to help minimize the slumping which by then was already under way. Today, the western half of the summit plateau is significantly lower than the eastern; this is the result of massive slumping, beginning about 1200 CE. This also caused the west end of the big building to collapse. It may have led to the abandonment of the mound's high status, following which various wooden buildings were erected on the south terrace, and garbage was dumped at the foot of the mound. By about 1300, the urban society at Cahokia Mounds was in serious decline. When the eastern side of the mound started to suffer serious slumping, it was not repaired.