This relatively wide pass enables for the easiest passage from northeastern Italy and northwestern Adriatic Sea to the Pannonian Plain, and had a very important strategic role in the past.

It has been proposed that the voyage of the Argonauts is based on the possibility to travel the Danube, the Sava, and the Ljubljanica rivers upstream, cross the Postojna Gate, and come to the Adriatic Sea downstream on the western side.

It was the central part of the ancient Illyro-Italic (or Italo-Illyrian) Gate between the southeastern Alps and the Kvarner Gulf, connecting northern Italy to the west and the Pannonian Plain to the east.

The Romans were well aware that their core territory was threatened by easy access through the Postojna Gate and they created a network of strategic roads, fortifications, and walls, the Claustra Alpium Iuliarum, to stop possible invaders.

[6] At the center of these fortifications was the fortress of Castra ad Fluvium Frigidum in the Vipava Valley controlling the Roman road between Aquileia and Emona.