The foundation of the city dates back to 181 BC, it was born as a Roman colony and later assumed the function of defence post. In 89BC it was transformed from a colony to a municipality and later under the rule of the Emperor Augustus it became the capital of the 10th region "Venetia et Histria". Its growing importance led to the reconstruction of the ancient centre and the construction of a fluvial port and an array of public buildings.

Aquileia's development was however at times hindered by infiltrations of barbaric troops ready to invade the imperial territory. When Diocletianus was nominated Emperor, Aquileia's former glory returned to fold and it developed into one of the Empire's largest and most important cities. It was here that a strong Christian community evolved, and in 313 AC Emperor Costantinus allowed these religious followers to profess their creed openly and Bishop Teodoro estabilished the first churches of the area.

The evangelisation of Istria, the Balcans, Hungry and the lands up to the Danube took off from here and the size of jurisdiction meant that Aquileia was to become one of the most important Christian bishoprics of all times. So much glory and wealth also meant new attacks. In 452 Attila the Hun arrived in the area, destroying all that lay in his wake. The territory's inhabitants were made to flee towards Grado and the lagoon islands. This was how the city of Venice was founded.

During the 6th century Italy was put under siege by the Longobards, a new kingdom was founded and Friuli was transformed into a Duchy in its own right with its capital set at Forum Iulii, while Aquileia was still patriarchal centre.

Abandoned by the Patriarchs, who preferred the cities of Cormons and later Cividale, Aquileia's glory was rekindled only by Charlemagne's intervention, allowing the return to the area of the Patriarch Massenzio. From the 9th cebtury onwards and during the course of the 10th and 11th centurie, the city of Aquileia rebuilt much of its past greatness and sparkle.

In 1077 the Emperor attributed feudal rights to the ruling Patriarch. His domain over the area lasted for many centuries to follow, even if it often clashed with the Venetian Republic's growing authority. In 1420 the Republic finally put a stop to patriarchal ruling throughout the area. From this moment onwards Aquileia was to witness a definite decline, resulting in the city becoming no more than a mere agricultural village. 1751 marked the year when the diocese was finally suppressed and from the break up of its territories the Udine Archbishopric was estabilished, ruling over the lands not only of Venetian domain but also those of Gorizia and other Austrian territories.