Venice is built on an archipelago of 117 islands formed by 177 canals in a shallow lagoon, connected by 409 bridges. In the old centre, the canals serve the function of roads, and almost every form of transport is on water or on foot. In the 19th century a causeway to the mainland brought the Venezia Santa Lucia railway station to Venice, and the Ponte della Libertà road causeway and parking facilities were built during the twentieth century. Beyond the road/rail land entrances at the northern edge of the city, transportation within the city remains (as it was in centuries past) entirely on water or on foot. Venice is Europe's largest urban car-free area. Venice is unique in Europe, in having remained a sizable functioning city in the twenty-first century entirely without motorcars or trucks.