1100 CE, is an area raised slightly higher still, on which was placed a building over 100 ft long, the largest in the entire Cahokia Mounds urban zone. Excavations on the southwest corner found that several large ceremonial buildings had burned around 1150 CE.

Botanical remains from Monks Mound suggest it was built much more quickly than previously thought, perhaps on the order of several consecutive decades, providing an alternative view of its construction history. Deep excavations in 2007 confirmed findings from earlier test borings,