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city, Anderson and Roane counties, eastern Tennessee, U.S. It lies in a valley between the Cumberland and Great Smoky mountains, about 20 miles (30 km) west of Knoxville, and is a part of that city's metropolitan area. A tract of land covering about 94 square miles (243 square km) was selected in 1942 as a major site of the U.S. wartime atomic energy program known as the Manhattan Project. Originally called Clinton Engineering Works for the nearby town of Clinton, it was chosen because it met the necessary requirements for security, labour, power, water, and transportation. The town, built by the U.S. Army Corps of Engineers behind security fences, reached a peak population of 75,000 by 1945 and included three facilities for research in building atomic weapons. In 1949 the city was opened to the public, and in 1955 the Atomic Energy Commission sold the property to the town's residents. The community voted to incorporate as a city in 1959.