St. Louis is one of the most important ports on the Mississippi River. Its population has declined since the 1950s, but it still has 319,000 residents as of 2013, with nearly 3,000,000 in its metropolitan area. It is home to four major sports teams, with only basketball not being represented in its sports franchises. It is also a cultural and tourist center for the Midwest, with the city serving as the home of the St. Louis Symphony, the Opera Theatre of Saint Louis, Fox Theatre, the Saint Louis Art Museum, and the Missouri History Museum. One of the city's most famous attractions is the Gateway Arch which was built as a monument to the westward expansion of the United States.