History: The Jefferson National Expansion Memorial is located in St. Louis, Missouri near the start of the Lewis and Clark Expedition. It was designated as a National Memorial by Executive Order 7523, on December 21, 1935, and is maintained by the National Park Service (NPS). The Gateway Arch was authorized on May 17, 1954. The park was established to commemorate several historical events:the Louisiana Purchase, and the subsequent westward movement of American explorers and pioneers; the establishment of the first cathedral and the first civil government west of the Mississippi River; the debate over slavery raised by the Dred Scott case. The memorial site consists of a 91-acre (0.36 km²) park along the Mississippi River on the site of the original city of St. Louis; the Old Courthouse, a former state and federal courthouse which saw the origins of the Dred Scott case; the 45,000-square-foot Museum of Westward Expansion; and the Gateway Arch, a steel catenary arch that has become the city's emblem. As the park entered the 21st century it is host to four million visitors each year, three-quarters of which enter the Arch or the Old Courthouse.