St. Charles Avenue (French: avenue Saint-Charles) is a thoroughfare in New Orleans, Louisiana, U.S. and the route of the St. Charles Streetcar Line. It is also famous for the dozens of mansions that adorn the tree-lined boulevard for much of the uptown section of the boulevard. It is named for St. Charles Borromeo, patron saint of Charles III of Spain, the monarch when France transferred the then-vast territory of Louisiana to Spain at the conclusion of the Seven Years' War in 1763. St. Charles Avenue is one of the chief Mardi Gras parade routes.