Complex sentence: Historically, they where the border between the duchies of Carinthia, Styria and Carniola, which was located on the Urška Gora (German "Ursulaberg").
Split into simpler sentences: Historically, they were the border between the duchies of Carinthia, Styria and Carniola. The tripoint was located on Uršlja gora (German "Ursulaberg").