The Città del Vaticano (Vatican City) the global centre of the Roman Catholic church, is a 44 ha enclave within the city of Rome whose status is defined by the Lateran Treaty of 1929. One of its links with the outside world is a 1.27 km railway from the San Pietro station of the Italian state railway system to a railway station within the city. It was built after the signing of the Lateran Treaty and was opened on 2 October 1934. Part of it is carried on a 143 m long viaduct of eight arches across the Gelsomino Valley. The station, situated in the Vatican gardens behind St Peter’s basilica and largely in white marble, was designed by the architect Guisseppe Momo. Part of it now houses the Vatican museum of numismatics and philately, and another part is a duty-free shop.
The railway is principally used for freight traffic. Pope John XXIII (1881-1963) travelled on the line on 4 October 1962, the first pope to do so, and in recent times its use has been encouraged by Pope Francis. A weekly train, a diesel multiple unit belonging to the state railway system, travels from the Vatican station to Albano Laziale from where a shuttle bus service takes visitors to the papal summer residence at Castel Gandolfo. One special occasions the train consists of vintage carriages headed by a steam locomotive of 1915.