 After the secular territory of the Patriarchs of Aquileia had been completely conquered by Venice in 1420, most of Istria belonged to "La Serenissima".The Austrian House of Habsburg only held a small territory in the interior of the peninsula around Pazin ("Mitterburg"), which it administered from its Carniolan duchy.The Habsburg rulers nevertheless added the title of a "Margrave of Istria" to their other titles, persisting until the dissolution of the Austro-Hungarian monarchy in 1918.