It consisted of three regions: the Margraviate of Istria in the south, Gorizia and Gradisca in the north, and the Imperial Free City of Trieste in the middle.

[1] The territory of the medieval Patriarchate of Aquileia had gradually been conquered by the Republic of Venice (Domini di Terraferma) until the early 15th century.

In the east, the Habsburg archdukes of Austria, based on the March of Carniola they held from 1335, had gained suzerainty over Istrian Pazin in 1374 and the port of Trieste in 1382.

They also purchased Duino and Rijeka (Fiume) on the northern Adriatic coast in 1474, and inherited more territory in Friuli when the Counts of Görz line died out in 1500.

The supremacy of the Republic of Venice in the Adriatic, and the Austrian archdukes' attention to the threat posed to them by an expanding Ottoman Empire, gave them little opportunity to enlarge their coastal possessions.

Incorporated into the Austrian Circle of the Holy Roman Empire, Görz, Trieste and Istria remained separately administered and retained their autonomy until the 18th century.

Emperor Charles VI increased the sea power of the Habsburg monarchy by making peace with the Ottomans and declaring free shipping in the Adriatic.

During the Napoleonic Wars, the Habsburg monarchy gained Venetian lands in the Istrian Peninsula and the Quarnero (Kvarner) Islands as part of the Treaty of Campo Formio of 1797.

It was formally divided into the Margravate of Istria and the Princely County (Gefürstete Grafschaft) of Gorizia and Gradisca with Trieste remaining separate from both.