Aquileia was founded as a colony by the Romans in 180/181 BC along the Natiso River, on land south of the Julian Alps but about 13 kilometres (8 mi) north of the lagoons.

The colony would serve as a citadel to check the advance into Cisalpine Gaul of other warlike peoples, such as the hostile Carni to the northeast in what is now Carnia and Histri tribes to the southeast in what is now Istria.

In fact, the site chosen for Aquileia was about 6 km (3.7 mi) from where an estimated 12,000 Celtic Taurisci nomads had attempted to settle in 183 BC.

However, since the thirteenth century BC, the site, on the river and at the head of the Adriatic, had also been of commercial importance as the end of the Baltic amber (sucinum) trade.

[8] The colony was established with Latin Rights by the triumvirate of Publius Cornelius Scipio Nasica, Caius Flaminius, and Lucius Manlius Acidinus, two of whom were of consular and one of praetorian rank.

[vague] Meanwhile, based on the evidence of names chiselled on stone, the majority of colonizing families came from Picenum, Samnium, and Campania, which also explains why the colony was Latin and not Roman.

In 148 BC, it was connected with Genua by the Via Postumia, which stretched across the Padanian plain from Aquileia through or near to Opitergium, Tarvisium, Vicetia, Verona, Bedriacum, and the three Roman colonies of Cremona, Placentia, and Dertona.

[citation needed] The construction of the Via Popilia from the Roman colony of Ariminium to Ad Portum near Altinum in 132 BC improved communications still further.

[citation needed] Meanwhile, in 169 BC, 1,500 more Latin colonists with their families, led by the triumvirate of Titus Annius Lucius, Publius Decius Subulo, and Marcus Cornelius Cethegus, settled in the town as a reinforcement to the garrison.

[11] The discovery of the gold fields near the modern Klagenfurt in 130 BC[12] brought the growing colony into further notice, and it soon became a place of importance, not only owing to its strategic military position, but as a centre of commerce, especially in agricultural products and viticulture.

[citation needed] Although the Iapydes plundered Aquileia during the Augustan period, subsequent increased settlement and no lack of profitable work meant the city was able to develop its resources.

Nevertheless, when in 168 Marcus Aurelius made Aquileia the principal fortress of the empire against the barbarians of the North and East, it rose to the pinnacle of its greatness and soon had a population of 100,000.

In 340, the emperor Constantine II was killed nearby while invading the territory of his younger brother Constans.At the end of the fourth century, Ausonius enumerated Aquileia as the ninth among the great cities of the world, placing Rome, Constantinople, Carthage, Antioch, Alexandria, Trier, Mediolanum, and Capua before it.

[15] The Roman inhabitants, together with those of smaller towns in the neighbourhood, fled en masse to the lagoons, where they laid the foundations of the cities of Venice and nearby Grado.

The patriarchate, despite being divided with a northern portion assigned to the pastoral care of the newly created Archbishopric of Salzburg, would remain one of the largest dioceses.

In the fourteenth century, the Patriarchal State reached its largest extension, stretching from the Piave river to the Julian Alps and northern Istria.

In 1445, the defeated patriarch Ludovico Trevisan acquiesced in the loss of his ancient temporal estate in return for an annual salary of 5,000 ducats allowed him from the Venetian treasury.

The Patriarchal State was incorporated in the Republic of Venice with the name of Patria del Friuli, ruled by a provveditore generale or a luogotenente living in Udine.

The site of Aquileia is believed to be the largest Roman city yet to be excavated and is on the UNESCO World Heritage List.

The National Archaeological Museum of Aquileia contains over 2,000 inscriptions, statues and other antiquities and mosaics, as well as glasses of local production and a collection.