High Quality Content by WIKIPEDIA articles! 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.