Now a village in northeastern Italy, near the Laguna di Marano, northwest of Trieste, but a very important city in the later Roman Empire. Its importance led to the Bishop being raised to metropolitan status, with ecclesiastical jurisdiction over northeastern Italy. The metropolitan later became known as the Patriarch of Aquileia, a consequence of the strong Byzantine influence in this region.
In 452 the city was sacked by the Huns, and never recovered the importance that it had had. In 568 the Lombards invaded Italy, and the Patriarch fled to the island of Grado in the lagoons south of the city. In 606 a new Patriarchate was established by the Lombards at Aquileia. Centuries of disputes followed, only resolved in the mid-12th century under Papal pressure, when the Patriarch of Aquileia gave up his claims over the lagoons and the Patriarch of Grado his claims over the northeastern mainland.
The Patriarch became head of a large principality, when the Emperor Henry IV gave him the March of Friuli in 1077, but the real beneficiaries were the local nobles, particularly the Count of Görz in the east. In the 15th century disputes between the Patriarch and the nobility led the latter to appeal to Venice for help, and after warfare in 1418-20, Venice took most of the old March, leaving the East, including Aquileia itself, under the care of the Counts of Görz. When they died out in 1500 they were succeeded by the Habsburgs.
The Patriarch had resided at Udine from 1258 but had perforce to return to Aquileia in 1420. The Patriarch remained the metropolitan over his ecclesiastical province, but relations between Venice and Austria were often strained, so in 1751 the Patriarchate was abolished and replaced by the Archbishoprics of Udine (for the Venetian lands) and Gorizia (for the Austrian). The Patriarchal palace became a ruin and the medieval town declined into a village.