The original chief city in the province was Roman Aquileia, but the Lombard capital of Friuli was Forum Julii, modern Cividale.

Along with the dukes of Spoleto, Benevento and Trent, the lords of Friuli often attempted to establish their independence from the royal authority seated at Pavia, though to no avail.

The Venetian territory around Forum Iulii, still devastated by the Gothic War, was the first in former Roman Italy to be conquered by the Lombards under their king Alboin in 568.

Before continuing on to penetrate Italy further southwards, Alboin left a large garrison at Cividale and placed the government of the district under his nephew and Marepaphias (shield-bearer), Gisulf as a dux, who was allowed to choose the faras or noble families with which he wished to settle the land.

It was bound by the Byzantine Exarchate of Ravenna to the south, where it did not have a coastline until later, and by a plain that led to the Pannonian Basin in the east, a perfect access point for invaders, such as the Avars and later the Magyars.

[3] Paul, who was originally from the duchy of Friuli also recounts in detail the betrayal of Romilda, Gisulf's wife, who handed the city of Cividale over to the Avars.

Gisulf II's sons, Tasso and Kakko had narrowly managed to escape the battle in which their father lost his life and assumed control of Friuli.

However Gisulf's other brothers, Romuald and Grimoald refused to accept Grasulf's superiority and relocated to the court of Arechis in the Duchy of Benevento.

Paul the Deacon recounts the reigns of Grasulf and his successor Ago very briefly, but they continued the war against the Byzantines and Opitergium was conquered in 642.

Under the leadership of the dukes of Friuli and Trent on various occasions these revolts gathered together the Arian and traditionalist (i.e. militaristic and expansionist) groups in opposition to the pacifist policy followed by the kings in Pavia, who were inclined to maintain the status quo with the Byzantines and the Papacy.

The Slavs achieved an easy victory, due to grave tactical errors on the part of the Lombards and exterminated almost the entire Friulian nobility.

As a result of the prestige that he had gained from these ventures, Rachis became king of the Lombards in 744, deposing Liutprand's successor Hildeprand after a few months of rule.

It is likely that in these years, when the Lombard kingdom was ruled by sovereigns of Friulian origin and the central power was particularly strong, that the autonomy of the duchy was very limited.

An indirect piece of evidence for this is the fact that Istria, which was conquered by Aistulf after he became king, was not annexed to the Duchy, but remained under direct royal control.