The B&O Railroad Museum is a museum exhibiting historic railroad equipment in Baltimore, Maryland, originally named the Baltimore & Ohio Transportation Museum when it opened on July 4, 1953. It has been called one of the most significant collections of railroad treasures in the world and has the largest collection of 19th-century locomotives in the U.S. The museum is located in the Baltimore and Ohio Railroad's old Mount Clare Station and adjacent roundhouse, part of the B&O's sprawling Mount Clare Shops site begun in 1829, the oldest railroad manufacturing complex in the United States.