The first Celtic area to be completely assimilated into the Roman system was also the first to have been conquered, Cisalpine Gaul. The situation here was untypical of the Roman Empire as a whole because of the removal of much of the Celtic population to make way for Roman and Latin settlers in the decades after the war with Hannibal. Elsewhere in the Roman Empire there was no great exodus of Roman settlers from Italy to the conquered provinces. Even the discharged veteran soldiers who settled in the colonies that were founded specially for them in the provinces (for example, Colonia Agrippina, modern Cologne) were mostly neither Roman nor even Italian but recruits from other provinces. However extensive the land confiscations may have been, the Romans did not succeed in removing all the Gaulish population. Celtic cults, like that of the Matronae (triple mother goddesses), continued into imperial times, as did Celtic personal names such as Boduac. The Celtic language continued to be spoken into the first century ad and even in the second century some northern Italians still spoke with a ‘Gallic’ accent. By this time though what remained of the Cisalpine Gauls had clearly long accepted Roman rule, as all of the region’s free population had been granted citizenship as early as 49 bc. Northern Italy developed a strong literary and poetic tradition in early imperial times and some of the greatest Latin poets, including Horace and Catullus, may have been of Celtic descent.
The coastal areas of Spain, which had long been influenced by the Greeks, Phoenicians and Carthaginians, were very quickly and completely Romanised. Though it was politically loyal to the empire, the Celtic interior was only superficially Romanised while the tribes of the mountainous north-west, the Gallaeci, Cantabri and Astures, remained largely uninfluenced by Roman civilisation. Romanisation was most obvious in religion. As throughout the empire, there was a rapid conflation of native and Roman cults. The nameless chief god of the Celtiberi was identified with Jupiter, for example, the underworld goddess Ataecina with Proserpina, and the native war god Tarbucelis with Mars. Religious images became Romanised, but they are often only thinly disguised native deities. Images of Venus and Diana are probably native mother goddesses. Worship of various nature spirits, such as the female xanas of Asturias, which were usually portrayed in Romanised fashion as nymphs and fauns, continued for centuries and they survive in local folklore to this day. All temples and shrines, whether of native or Roman deities, were built in Classical styles. Religious beliefs were least Romanised in Galicia. In most of imperial Spain, Roman deities eventually came to outnumber native ones. In the north-west, however, the numbers were about equal. The eastern mystery cults of Isis, Cybele and Mithras spread to Spain, and in the third century Christianity became important. The Celtic cults declined as Christianity took over in the fourth century, and the latest known inscription mentioning a Celtic god is to the otherwise unknown Erudinus, which was made at Santander in 399.
The old Celtic tribal identities still survived in north-west Spain even in the fifth century, where the Vaccaei, Gallaeci, Astures and Cantabri all resisted the invading Visigoths and Suevi, while there was no resistance in the more Romanised areas. Kin-based clans (called gentes by the Romans) also persisted throughout the period of Roman rule. In the north-west, the pre-Roman settlement pattern continued unchanged. The Romans saw cities as being synonymous with civilisation, but in north-west Spain their attempts at urbanisation failed and Celtic castros (hillforts) remained occupied until the end of the Roman period and beyond. One, Castro de Mohias near Oviedo, was occupied continuously from the Iron Age until the sixth or possibly even the ninth century. No Roman-style public buildings, such as theatres, are known from the area. Round stone huts continued to be built even in what passed for towns. Celtic symbols such as sun discs were used on funerary stelae (upright stone slabs with carvings or inscriptions) and pre-Roman decorative styles re-emerged in late Roman times, showing a conscious revival of identification with the Celtic past. Tores were still made well into the imperial period, and Celtiberian type javelins continued to be used even in the thirteenth century. The majority of personal names in the north-west continued to be Celtic throughout Roman rule. How long Celtic languages survived after the Roman conquest is unclear. Certainly Hispano-Celtic was still in ordinary use in the first century ad and, as modern Portuguese and Galician contain many words of Celtic formation, it must have survived until late Roman times when Latin began to break up into the precursors of the modern Romance languages. It is clear that it was not Roman conquest that killed Celtic Spain but Christianity and the subsequent Germanic and Moorish invasions.