Claustra Alpium Iuliarum (Latin for 'Barrier of the Julian Alps'; hereby, the term Julian Alps refers to the wider mountainous and hilly region from the Julian Alps to the Kvarner Gulf) was a defense system within the Roman Empire between Italia and Pannonia that protected Italy from possible invasions from the East.[1] It secured the Postojna Gate, the land link between the eastern and western part of the empire, and thus the Claustra represented an inner border defense of the empire.[2] Unlike a linear rampart, the Claustra consisted of a series of interconnected fortifications with its center at Castra ad Fluvium Frigidum (in the area of today's town of Ajdovščina, the Vipava Valley); other important fortresses were Ad Pirum on today's Hrušica Plateau and Tarsatica, now a part of the city of Rijeka. They had been governed from the town of Aquileia.
- ^ Potocnik AJ. "Claustra Alpium Iuliarum". Archived from the original on May 24, 2010. Retrieved July 21, 2010.
- ^ C.R.Whittaker. Frontiers of the Roman empire. A social and economic study. Baltimora & London, 1997. p. 197.