Rock Island is the county seat of Rock Island County, Illinois, United States. The population was 39,684 at the 2000 census. It is one of the Quad Cities, along with neighboring Moline, East Moline, and the Iowa cities of Davenport and Bettendorf. The original Rock Island, from which the city gets its name, is the largest island in the Mississippi River and is now known as Arsenal Island. The Chicago, Rock Island & Pacific Railroad was founded here in 1851 and was known as the Rock Island Line. The railroad was liquidated in bankruptcy in 1980. Rock Island is also home to the Rock Island Arsenal on Arsenal Island. It is an active factory producing ordnance and weapons components for the U.S. Army. The Arsenal provides 6,000 civilian jobs for the local area. The south shore of Rock Island, on the Rock River, is where the former village of Saukenuk was located, the birthplace of the warrior Black Hawk. The Black Hawk State Historic Site includes much of the site of the original village of Saukenuk. The park includes a museum and a number of hiking trails along the Rock River and in surrounding woods. Due to its geography, Rock Island has a rich history of bridge-building. The first railroad bridge across the Mississippi River was built between Arsenal Island and Davenport in 1856. Steamboat pilots of the day, fearful of competition from the railroads, considered the new bridge “a hazard to navigation”. Two weeks after the bridge opened, the steamboat Effie Afton rammed part of the bridge and set it on fire. Legal proceedings ensued—with a young lawyer named Abraham Lincoln defending the railroad. The lawsuit was appealed went to the Supreme Court, and was decided in favor of Lincoln and the railroad. Although the original bridge is long gone, a monument exists on Arsenal Island marking the Illinois side. Bridge Street, in Davenport, is the location of the Iowa side. Lock and Dam No. 15 and the Government Bridge are now located just southwest of the original bridge site. The Government Bridge, completed in 1896, is notable for having two sets of railroad tracks above the car lanes. It is one of only two bridges in the world with this feature. Lock and Dam No. 15, completed in 1934, is the largest roller dam in the world. The dam is only designed for navigation, not flood control. During flood season, the rollers are raised, unleashing the full flow of the water. Three other bridges span the river between Rock Island and Davenport. The Crescent Rail Bridge is a railroad-only bridge, completed in 1899. The Centennial Bridge was completed in 1940 for autos only. The newest bridge is the Interstate 280 bridge, completed in 1973. On the south side of the city, overlooked by the Black Hawk State Historic Site, is a crossing of the Rock River to Milan, Illinois. This set of bridges also crosses the historic Hennepin Canal. A new bridge was completed in 2007 between 3rd Street Moline/southeast Rock Island and Milan, Illinois. It expedites the trip to Milan, the airport, and points south on U.S. Route 67.