The Old Gateway or Roman Arch is not a Roman triumphal arch, as was once presumed, but a representative main entrance to the centre of the Late Antique command compound of the Roman Tarsatica, an ancient town on whose ruins the medieval Rijeka was built. Rijeka’s common people were right in calling this ancient monument simply the Gateway, while the name Roman Arch has been gradually accepted since Classicism, when it started to be documented and researched.  The profiled formwork of the Arch is only partially preserved to be built into the houses of medieval Rijeka, the remaining parts have long fallen off or been blown up. This Principia was the main headquarters, the supply base and the starting point of the Alpine enclosure, composed of dozens of kilometres of defensive walls, towers, guard-stations and larger forts mostly located on communication points and elevated ground for the purpose of blocking the barbarian incursions towards Italy as the centre of the Roman Empire.