The Gateway Arch is located in downtown St. Louis, Missouri, along the Mississippi Riverfront. The Arch is a monument that commemorates the Western expansion of the United States and is our Nation's tallest monument. The Arch is part of the Gateway Arch National Park, formerly known as Jefferson National Expansion Memorial, a 91 acre park that is one of the 429 National Park Sites in the US. It also includes the Old Courthouse and the Museum at the Gateway Arch. A visit to the Arch is not complete without riding one of the innovative trams to the top.