Claustra Alpium Iuliarum (Latin: "Barrier of the Julian Alps") was a defense system within the Roman Empire between Italia and Pannonia that protected Italy from possible invasions from the East. 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. Contrary to a linear limes the Claustra consisted of a series of interconnected fortifications with its center at Ad Pirum at today's Hrušica.