Birdswold Roman Fort, from which a road led north to the outpost fort at Bewcastle has some of the best Roman remains to found in this historic region. According to early historians Fordum and Boethius Carlisle existed before the arrival of Romans in Britain and was one of the strongest British towns at the time. In the time of the emperor Nero it was said to have burned down. The town was named Luguvalion or Luguwaljon, meaning 'strength of the god Lugus'. This was later Latinised into Luguvalium and later still was derived to Caer-luel (Caer meaning fort in Brythonic).
By the year 73 CE (AD) the Roman invasion of Britain had reached the River Eden and a fort was built that winter at a strategic point overlooking the confluence of the River Caldew with the Eden, where Carlisle Castle stands today. The created civitas was the only walled-town in the entire north west region of Roman Britain, for this reason it is reasonable to assume that the settlement did exist and served as a tribal centre for the Carvetii before Roman occupancy, following the pattern of other civitates made by the Romans.
In 79AD the two main Roman generals active in north Britain, Gnaeus Julius Agricola and Quintus Petillius Cerialis, advanced through the Solway area as they continued their campaign further north. As a result it is likely greater control was achieved at Carlisle over anti-imperialist groups. Something which is signified by the fact the fort at Carlisle was able to be refurbished in 83AD using oak timbers from further afield rather than the local Alder. At this time the fort was garrisoned by a 500 strong cavalry regiment, the ala Gallorum Sebosiana. ( See Hadrian’s Wall)
Source & More Information: Wikipedia, Carlisle, Cumbria, http://en.wikipedia.org/wiki/Carlisle,_Cumbria