The first settlements date back to the period between the 9th and 7 Century BC Between 42 and 40 BC, the city was conquered by the Romans and occupied. Under Augustus Octavian happened the foundation of the colony Julia Concordia as an outpost against the Northeast.
The facility was secured, roads were expanded as well as the channels were made navigable. Concordia developed into an important city with its own amphitheater, temples and burial grounds. It was administered by a Duovirat (rule of two persons) that spoke right, and a second Duovirat that was used as Aedili (originally temple keeper).
The former looked after the jurisdiction, just as the consuls in Rome did, the second took care of nutrition, of the general economic situation and the public administration, such as road and building houses.
From the 3rd century AD the city had the important role to repel the barbarian invasions. At this time the local arms factory was made up for the production of arrowheads (sagittae), which ultimately gave her name Concordia Sagittaria. The enemies invasions and a devastating flood in 589 ushered in the downfall of Concordia, in parallel with the decline of the Roman Empire.
452, the Huns under Attila devastated all major centers in Friuli as Aquileia, Altino, Padova and Verona. 568 the Longobards invaded, in the second half of the 9th Century followed by the Franks. In these horrible times the church was left as the only place in the social, civic and cultural life.
By an essay by the Bishop of Aquileia Cromazio (to 389) it is shown that Concordia was to receive the relics of some apostles from the East, destined for a basilica and its first bishop.
After the collapse of the pre-Christian basilica a second was built between the end of the 9th Century and early 10th Century, while the basilica from today rests on the ruins of a third basilica built in the 11th Century. 4 basilicas right at the same spot, only separated by time.
During the Renaissance, the city experienced an economic boom again, but it was followed by bitter poverty and a general decline. The main reason for this serious decline was the near of the unhealthy swamps and bogs in the area.
Only since the mid-20th Century the city recovered slowly, thanks to the draining of the marshes and reclamation of the surrounding country.