Rock Island, city (1990 pop. 40,552), seat of Rock Island co., NW Ill., on the Mississippi and Rock rivers, adjacent to Moline and opposite Davenport, Iowa; inc. 1841. These three cities, with Bettendorf, Iowa, are called the Quad Cities. Rock Island is a trade, transportation, and industrial center. Machinery, metal and wood products, and clothing are among its many manufactures. Railroad maintenance is also an important industry. Rock Island is the seat of Augustana College, and Black Hawk State Park adjoins the city. On a 1,000-acre (405-hectare) island in the Mississippi River is a huge U.S. arsenal (est. 1862), one of the largest manufacturing arsenals in the world and a major source of local employment. Arsenal Island was fortified by the British in the War of 1812 and by the Americans in 1816. In 1833, George Davenport built a palatial house there that still stands. During the Civil War, Arsenal Island was the site of a large northern military prison. A Confederate cemetery and a national cemetery are there. Bridges connect Arsenal Island, Rock Island, Davenport, and Moline.