Claustra Alpium Iuliarum

Claustra Alpium Iuliarum is a Roman fortification system spread across the Julian Alps with stone walls, watchtowers, and military outposts linked together. The defense line runs through multiple mountain passes to create a connected barrier.

The system was built between the 3rd and 5th centuries to protect the Roman Empire from invasions by controlling mountain passages. It marked the empire's eastern boundary toward Italian territory.

The remains of this fortification system demonstrate Roman military engineering methods through preserved walls reaching 8 meters high and 2 meters thick.

Visitors can explore the archaeological site through marked walking trails connecting different sections of the ancient defense line. The trails run through mountainous terrain between Rijeka and the Ravne Gorge.

Ad Pirum, a fortress within the system, had facilities to temporarily house tens of thousands of soldiers, though only a few hundred stayed there normally. This contrast shows how the Roman military could adjust its forces based on threat levels.