The counts of Dießen-Andechs (1100 to 1180) obtained territories in northern Dalmatia on the Adriatic seacoast, where they became Margraves of Istria and ultimately dukes of a short-lived imperial state named Merania from 1180 to 1248.

The noble family originally resided in southwestern Bavaria at the castle of Ambras near Innsbruck, controlling the road to the March of Verona across the Brenner Pass, at Dießen am Ammersee and Wolfratshausen.

He probably married a daughter of Duke Frederick I of Upper Lorraine; his descendant Count Berthold II (d. 1151), from about 1100 residing at Andechs, is credited as the progenitor of the comital dynasty.

Berthold II had inherited the family's Bavarian territories but also acquired possessions in the adjacent Franconian region, where about 1135 he had the Plassenburg built near Bayreuth and established the town of Kulmbach.

He served as vogt of Benediktbeuern Abbey and by marriage with Sophie, daughter of Margrave Poppo II, came into property of lands in the March of Istria and Carniola.