Monks Mound is the largest Pre-Columbian earthwork in America north of Mesoamerica. Located at the Cahokia Mounds UNESCO World Heritage Site near Collinsville, Illinois, its size was calculated in 1988 as about 100 feet (30 m) high, 955 feet (291 m) long including the access ramp at the southern end, and 775 feet (236 m) wide. This makes Monks Mound roughly the same size at its base as the Great Pyramid of Giza (13.1 acres / 5.3 hectares). Its base circumference is larger than the Pyramid of the Sun at Teotihuacan.

Unlike Egyptian pyramids which were built of stone, the platform mound was constructed almost entirely of layers of basket-transported soil and clay. Because of this construction and its flattened top, over the years, it has retained rainwater within the structure. This has caused "slumping", the avalanche-like sliding of large sections of the sides at the highest part of the mound. 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.

A mound is a general term for an artificial heaped pile of earth, gravel, sand, rocks, or debris. The most common use is in reference to natural earthen formation such as hills and mountains, particularly if they appear artificial. The term may also be applied to any rounded area of topographically higher elevation on any surface. Artificial mounds have been created for a variety of reasons throughout history, including ceremonial (platform mound), burial (tumulus), and commemorative purposes (e.g. Kościuszko Mound).

In the archaeology of the United States and Canada, the term "mound" has specific and technical connotations. In this sense, a mound is a deliberately constructed elevated earthen structure or earthwork, intended for a range of potential uses. In European and Asian archaeology, the word "tumulus" may be used as a synonym for an artificial hill, particularly if the hill is related to particular burial customs.

While the term "mound" may be applied to historic constructions, most mounds in the United States are prehistoric earthworks, built by Native American peoples. Native Americans built a variety of mounds, including flat-topped pyramids or cones known as platform mounds, rounded cones, and ridge or loaf-shaped mounds. Some mounds took on unusual shapes, such as the outline of cosmologically significant animals. These are known as effigy mounds. Some mounds, such as a few in Wisconsin, have rock formations, or petroforms within them, on them, or near them.