The activities of Julius Caesar (100-44 BC) as proconsul in Transpadane was very intense, and we know that Cividale, the ancient “Forum Iulii”, was founded by the great Roman leader, along with other cities, as Concordia, for example, in the same area of Friuli. About “Forum Iulii”, in ancient times,  we do not have many evidences. Pliny the Elder [23-79 AD] (“Naturalis Historia”, III, 23, 130-131) was very dismissive about the “ X Regio Augustea”, and spoke quickly  of “Forum Iulii” and its surroundings, saying that they were  places “Quos scrupolosius dicere non attineat” (“about which wasn't the case to say scrupulously”). Even Ptolemy (100-175 AD), the great geographer of the ancient world, was quick to mention Cividale, simply quoting a Roman colony that he called, in Greek, "Foros Isulios”. For more detailed information on "Forum Iulii", which was situated at the point where today there is Cividale, on the right bank of the river Natisone, one must wait for the Lombard period.

However the city was located in an area that was directly connected with the valleys of Isonzo and Idria, and therefore close to mountain passes of the Julian Alps. The geographical position coincided with an occupation of populations since the Neolithic. In pre-Roman times, the area was probably inhabited by Celtic peoples, who came into contact with Rome around the third century BC. Initially, some scholars had thought, by name "Iulii", which Cividale had been founded by Augustus (63 BC-14 AD), but studies have also shown that the founder of Cividale was Julius Caesar who, during his proconsulship, strengthened  with various "Castra" ("fortified cities") some strategic points of the territory in order to curb the barbarian incursions (See Pier Saverio Leicht,  “Forum Iulii”, in “Memorie Storiche Forogiuliesi”, 30, 2, 1934: 107-108).

Cividale was thus called "Iulii" in honor of "Julius" Caesar; but as regards the first part of the name, "Forum", we remember that Caesar, giving the title to his new city, wanted, somehow, emphasize the “legal” importance of it. Indeed, the title of "Forum" for a city,  meant a sort of "promotion", as the Romans recognized that in it  there was a large influx of people, especially on market days; during  these days worked the Court, and the Governor of the Province gave audience to the people, in fact, in Latin, "Forum agere" means precisely "to hold hearing." Hence the etymology of "Forum Iulii” is clear, meaning “city where "Iulius (Caesar) held hearings ('Forum')", to the people in Court. In the Middle Ages Cividale was instead called simply "Civitas", meaning "city"; Cividale was then briefly called "The City", meaning that it was “the most important city”, or “the city of all cities.” The modern name, "Civi-dale," derives from the fact that, from the ninth century, it also took the name of "Civitas Austriae", "City of Austria", hence the current name.

While the information about the ancient age are scarce, since the Lombard conquest of Cividale, we possess substantial historical data, because Cividale was the native land of Paul the Deacon (720-799), who sent us very interesting information about his hometown, to which he was very fond. During the Lombard period, Cividale "[...] followed then to Aquileia, as Paul Deacon says, and it became the center of all the ancient 'Venetia'. Perhaps in Cividale, for some time, there was also the Arian Bishop, while the Catholics depended on the Patriarch of Aquileia [...]" (See G. Fogolari, “Cividale del Friuli”, Italian Institute of Graphic Arts, 1908:14, 40). In the fifth century AD, then, after the invasions of the Avars and the destruction of Aquileia by the Huns, Cividale increased its number of citizens and strategic importance. Come the Lombards in the seventh century AD, it was the first capital of the Lombard duchy of Italy headed by the Duke Gisulf (VI century), grandson of Alboin (530-572). It was at that time that it changed its name  “Forum Iulii” to  “Civitas”, which later became “Cividale”.

Cividale became a bishopric in 737 and the “caput Venetiae”( “Capital of 'Venetia'”), inheriting the title from Aquileia. Under the dominion of the Franks, Cividale was a duchy and then a "marca", meaning the name  that it was the head of a vast region. The Duke of Friuli Berengar I (845-924) became also king of Italy (888-924) and emperor in 915. From the twelfth century, it was an independent municipality and a center with an important market, and since then it was the greatest political and commercial center of the whole Friuli, much to gain by  Emperor Charles IV (1316-1378) the opening of the University, in 1353 . In 1238 the Patriarchs moved to Udine and therefore there were rivalries and struggles with this city. In 1419, during the war with Venice, to drive the Hungarian King Sigismund (1387-1437) the siege, Cividale surrendered to Venice. In the sixteenth century it was fought between the Empire and Venice in July 1509;  Cividale was besieged by the imperial troops of the Duke of Brunswick, but the citizens managed to break the siege, forced to flee the German army. After the war Cividale was under the Venetian rule. With peace of Worms (1530), Cividale lost the Castle of Tolmin, and the mercury mines of Idria. Under Venetian rule, it was a great center of learning. In 1797, with the Treaty of “Campoformio” between Napoleon (1769-1821) and Austria, Cividale passed to the Habsburg Empire,  to which, after the brief period when it was part of the Napoleonic Kingdom of Italy, was confirmed by the Congress of Vienna (1815). Between 1848 and 1866 there was the presence of a vibrant “Risorgimento” movement, and in 1866, after the Third War of Independence, it was annexed to the Kingdom of Italy with the Veneto and Friuli.