Prior to the invasion, significant fortifications known as the Rupnik Line were constructed along the Italian and German borders, within what became the 7th Army's area of operations. Along the frontier with Italy, mutually supporting bunkers were established on forward slopes of the mountain ranges behind a belt of obstacles. The main positions followed a line from Mount Blegoš south-south-east through Hlavče Njive, Žirovski Vrh, Vrh Svetih Treh Kraljev, Zaplana, Mount Slivnica, Grahovo, and Lož to Petičak. To the north of Mount Blegoš, positions ran behind the lines of the Selška Sora and Sava Bohinjka rivers. Fortifications were also established in the mountainous Gorski kotar region between Karlovac and Fiume on the upper Adriatic coast. Along the German border, the Yugoslavs concentrated on preparing to block the passes through the Karawank and Kamnik Alps, and built bunkers behind obstacles along the routes leading south from the border towards Dravograd, Maribor and Ptuj. Preparations were also made to block routes north of the Drava and along the southern banks of the Mura and Drava. These fortifications were to be manned by border guard units, and were not the responsibility of the 7th Army.