Lock and Dam No. 15 is a lock and dam located on the UpperMississippi River. It spans the river between Rock Island, Illinois and Davenport, Iowa. Lock and Dam 15 is the largest roller dam in the world, its dam is 1,203 feet (366.7 m) long and consists of nine 109 feet (33.2 m) non-submersible, non-overflow roller gates and two 109 feet (33.2 m) non-submersible overflow roller gates. It is unusual among the upper Mississippi River dams in that it has only roller gates, has different sizes and types of roller gates, it is not perpendicular to the flow of the river and is one of the few facilities that has a completed auxiliary lock. The main lock is 110 feet (33.5 m) wide by 600 feet (180 m) long and its auxiliary lock is 110 feet (34 m) wide by 360 feet (110 m) long. In 2004, the facility was listed in the National Register of Historic Places as Lock and Dam No. 15 Historic District, #04000175 covering 3,590 acres (1,450 ha), 2 buildings, 9 structures, and 1 object.