Claustra Alpium Iuliarum

Forum Iulii

Tarsatica

Castra ad Fluvium Frigidum

Nauportus

Ad Pirum

Emona

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Location of Claustra Alpium Iuliarum outposts with modern national borders of Slovenia and neighbouring countries.

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.