The first historical date related to the arrival of the Carni is 186 BCE, when some 50,000 Carni, composed of armed men, women and children, descended towards the plains (in which they previously used to winter) and on a hill they founded a stable defensive settlement, Akileja.
Roman Republic troops forced the Carni back into the Alps, destroyed their settlement, and founded a Roman defensive settlement at the northeast boundary. The new settlement was named Aquileia, after the former Celtic name Akileja. The triumvirs that founded that settlement were Publius Scipio Nasica, Caius Flaminius, and Lucius Manlius Acidinus.
In order to stem the Roman expansion and to acquire the fertile and more hospitable plains, the Carni tried to form alliances with the Histrian, the Iapydes, and the Taurisci Celts. As Rome, in turn, was more and more becoming aware of the impending danger coming from the Carni and as it wanted to accelerate its own expansion, it sent to the north-east the legions of consul Marcus Aemilius Scaurus, who finally defeated the Carni in the battle of 15 November 115 BCE.
The Carni submitted to the Roman Republic in the 2nd century BCE, accepting its commands and its concessions. They received then the permission to populate and colonize the plain between the Julian pre-Alps and the Livenza river they had already tried to occupy previously in conflict with both the Romans and Veneti.
In the meantime, Aquileia enlarged its importance. It became a Municipium Romanum in 90 BCE. It was an important commercial and hand-craft production centre. Also it was the main port on the Adriatic sea and a garrison settlement.
In Late Antiquity, under the pressure of Germanic and Slavic peoples, the mountainous area populated by the Latinized Carni shrank gradually narrowing to Carnia and Friulian plains alone, and accepting migration contributions from Carniola, Carinthia and from other areas of the Empire. The phenomenon probably stabilized under the Lombards' domination of Friuli.