The Basilica of Saint Louis, King of France, formerly the Cathedral of Saint Louis, and colloquially the Old Cathedral, was the first cathedral west of the Mississippi River and until 1845 the only parish church in the city of St. Louis, Missouri. It is one of two Catholic basilicas in St. Louis, and it is named for King Louis IX of France, also the namesake for the city of St. Louis.
The current structure is located near the historic riverfront of St. Louis, surrounded by but not a part of the Gateway Arch grounds. Because of the historical significance of the church, it was left intact while all neighboring buildings were demolished to make way for the Gateway Arch. The basilica currently serves as a personal parish church rather than a territorial parish church, and therefore ranks 177th of 196 churches in number of Catholics per church in the Archdiocese of St. Louis.
However, because of its historical significance (and its location along the Mississippi River near the iconic Arch), the basilica remains a popular church for marriage ceremonies in the archdiocese (ranking second of 196 churches) and a popular tourist destination.