An ancient region of Europe, corresponding to modern France, Belgium, the south Netherlands, south-west Germany, and northern Italy. The area was settled by groups of Celts, who had begun migration across the Rhine in 900 bc, spreading further south beyond the Alps from 400 bc onwards and ousting the Etruscans. The area south of the Alps was conquered in 222 bc by the Romans, who called it Cisalpine Gaul. The area north of the Alps, known to the Romans as Transalpine Gaul, was taken by Julius Caesar between 58 and 51 bc, remaining under Roman rule until the 5th century ad. Within Transalpine Gaul the southern province, parts of which had fallen to the Romans in the previous century, became known as Gallia Narbonensis.