CAHOKIA MOUND, THE. The largest prehistoric Ameri can earthwork north of Mexico, one of a group formerly number ing 45 considerable mounds (not including a great number of smaller ones), standing in Illinois, 6 m. east of St. Louis, Mo. The great mound is a quadrangular pyramid 998 by 721 ft., by 99 ft. in height, with a terrace, 3o ft. high, extending outward about zoo ft. from one side and with a width of 500 feet. The area of the base is over 16 acres, and its contents have been estimated at 21,690,000 cu. ft., including the terrace; hence, with the means available to prehistoric Indians, it is estimated that it would have taken 1,000 persons nearly five years to build the main earthwork alone. The mound is named from a tribe which oc cupied the neighbourhood in historic times.