Unlike Egyptian pyramids which were built of stone, the platform mound was constructed almost entirely of layers of basket-transported soil and clay.

Its designed dimensions would have been significantly smaller than its present extent, but recent excavations have revealed that slumping was a problem even while the mound was being made.

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.

[3] 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.

[2] 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.

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.

The River L'Abbe Mission served a small Illiniwek community, until they were forced to abandon the area by rival tribes about 1752.

During their short stay in the area, which lasted until 1813, Henry Brackenridge visited the site and published the first detailed description of the largest mound.

One of the biggest began in the 1960s, when Nelson Reed, a local businessman and historian of native cultures, obtained permission to conduct excavations.

In 1970, Reed returned to work at the mound, and adopted a new strategy: scraping away the topsoil from several 5 m2 (54 sq ft) patches with a backhoe, to a depth of around 60 cm (24 in).

Further backhoe work in 1971 confirmed the shape of the presumed temple at over 30 m (98 ft) long, the largest building found at Cahokia.

This technique was opposed by professional archaeologists because it destroyed several hundred years of stratification over most of the mound's summit, which was the evidence by which they could place and evaluate artifacts and construction.

[10] From the time the original urban society collapsed, the great mound became overgrown with trees, the roots of which helped stabilize its steep slopes.

In 2007, backhoes were used to dig out the entire mass of earth from this slump and another at the northwest corner, to a level beyond the internal slippage zone.