Cahokia is the site of one of the largest prehistoric communities in the Americas. The site, near St. Louis, Missouri, consists of a group of more than 100 earthen mounds over an area of about 6 square miles (16 square kilometers). Indigenous (native) members of an early North American civilization called the Mississippian culture built and occupied Cahokia beginning about A.D. 900. Archaeologists estimate that 10,000 to 20,000 people may have lived at Cahokia at its peak, between about 1050 and 1150. Many more people lived in surrounding villages and farms. Some archaeologists believe that, in the Americas, only Teotihuacán, a city in ancient Mexico, was larger (see Teotihuacán).
Cahokia lies near where the Mississippi, Missouri, and Illinois rivers meet. People in the region grew maize, squash, pumpkin, and other crops on the fertile soils of the flood plains surrounding these rivers. They supplemented their diet by hunting, fishing, and gathering edible wild plants from nearby wetlands and forests.
Cahokia’s location also made it an important trading center. Archaeologists have discovered objects at Cahokia fashioned from materials that came from as far as 1,000 miles (1,600 kilometers) away. These include ornaments and ceremonial objects fashioned from sea shells, shark teeth, copper, and mica.
A large earthwork structure called Monk’s Mound occupies the center of the Cahokia site. The mound is the largest prehistoric earthwork in the Americas. It covers about 16 acres (6 hectares) at the base and has four levels rising to a height of 100 feet (30 meters). Archaeologists have determined that a large structure once stood at the top of the mound. This structure was about 48 feet (14.6 meters) wide and 104 feet (31.7 meters) long and was probably the residence of Cahokia’s chief ruler.
Many other mounds at Cahokia are rectangular with flat tops. These mounds served as platforms for temples, ceremonial buildings, and residences of the leaders. Conical (cone-shaped) mounds and long, narrow earthworks called ridgetop mounds were used for burials and to mark important locations. Most mounds at Cahokia show signs that they have been enlarged several times.
Archaeologists have identified several large circles of wooden posts at Cahokia that may have served as solar calendars. The sun rises above particular posts during the solstices, which mark the beginning of summer and winter, and the equinoxes, which mark the beginning of spring and autumn. During the 1200’s, the residents of Cahokia built a log palisade (wooden wall) nearly 2 miles (3.2 kilometers) long surrounding the central mounds. Archaeological evidence indicates that the palisade was rebuilt several times. Archaeologists are not certain if the palisade was built to defend Cahokia’s rulers against local uprisings or against raiders from a greater distance.
Cahokia’s residents gradually abandoned the site after 1250, and it was uninhabited by 1400. Archaeologists are not certain why Cahokia was abandoned, but they think several reasons are likely. Factors that may have contributed to the decline include drought, crop failures, ineffective leadership, and warfare. In the 2020’s, researchers ruled out flooding and the destruction of forests as possible causes for Cahokia’s decline. Some Indigenous groups of the region today are probably descendants of the people of Cahokia.
Cahokia Mounds State Historic Site was registered as a United States National Historic Landmark in 1964. In 1982, the United Nations Educational, Scientific and Cultural Organization (UNESCO) recognized Cahokia as a World Heritage Site.
See also Mound builders (Mississippian Period).
