Today, the city is small (about 3,500 inhabitants), but it was large and prominent in Antiquity as one of the world's largest cities with a population of 100,000 in the 2nd century AD.

Aquileia was founded as a colony by the Romans in 180/181 BC along the Natiso River . The colony served as a strategic frontier fortress  intended to protect the Veneti, faithful allies of Rome during the invasion of Hannibal. It was also important for the commercial trade of the Baltic amber (sucinum). The discovery of the gold fields near the modern Klagenfurt in 130 BC^[8] 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 center of commerce, especially in agricultural products and viticulture. 

In 90 BC, the original Latin colony became a municipium . Caesar visited the city several times. Augustus was the first of a number of emperors to visit Aquileia, in the 12‑10 BC. It was the birthplace of Tiberius' son by Julia. The Roman poet Martial also praised Aquileia. 

In terms of religion, the populace adopted the Roman pantheon, although the Celtic sungod, Belenus, had a large following. Jews practiced their ancestral religion and it was perhaps some of these Jews who became the first Christians. Meanwhile, soldiers brought the martial cult of Mithras. 

 

In 168 Marcus Aurelius made Aquileia the principal fortress of the empire against the barbarians of the North and East .
ARCHEOLOGICAL AREA

At the end of the 4th 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. However, such prominence made it a target and Alaric and the Visigoths besieged it in 401, during which time some of its residents fled to the nearby lagoons. Alaric again attacked it in 408. Attila attacked the city in 452. During this invasion, on July 18, Attila and his Huns so utterly destroyed the city that it was afterwards hard to recognize its original site. The fall of Aquileia was the first of Attila's incursions into Roman territory; followed by cities like Mediolanum and Ticinum.^[10] The Roman inhabitants, together with those of smaller towns in the neighborhood, fled en masse to the lagoons, and so laid the foundations of the cities of Venice and nearby Grado.

Yet Aquileia would rise again, though much diminished, and continue to exist until the Lombards invaded in 568; the Lombards destroyed it a second time in 590.