The term Natisone Valleys (Nediške doline in Slovenian, Vals dal Nadison in Friulian) indicates the area that includes the four valleys of the Natisone, Alberone, Cosizza and Erbezzo rivers. It forms a natural link between Cividale del Friuli (the ancient Forum Iulii) and the Isonzo volley, and was inhabited historically by a Slovenian speaking community. These four valleys, located near the Italian-Slovenian border at the eastern extremity of Friuli-Venezia Giulia, form the southern spine of the Julian Prealps. Mount Matajur (1,641 metres), whose summit dominates the plains below, is the symbol of this region.

Matajur, also known as Monte Re and Baba in the local Slovenian dialect, is a mountain of the Julian Prealps with a height of 1,641 metres. It is situated in the eastern part of the Friuli region, where it overlooks the city of Cividale.
Although of modest height, the mountain is easily recognised from the Friulian plain by its conical shape, and is both the most representative feature and the symbol of the Natisone Valleys.

It is not possible to say with any precision when the mountain was formed, since it is largely composed of sedimentary material laid down in the periods between the Jurassic and Upper Cretaceous ages. Drilling operations on its slopes have revealed traces of gold with zinc, silver and native mercury.