The Keystone Corridor is a 349-mile (562 km) railroad corridor between Philadelphia and Pittsburgh, Pennsylvania, that consists of two rail lines: Amtrak and SEPTA's Philadelphia-to-Harrisburg main line, which hosts SEPTA's Paoli/Thorndale Line commuter rail service, and Amtrak's Keystone and Pennsylvanian inter-city trains; and the Norfolk Southern Pittsburgh Line. The corridor was originally the Main Line of the Pennsylvania Railroad.