The capital of Gallia Narbonensis was Narbo Martius, modern Narbonne in southern France. It was founded in 118 BCE when the Romans built the Via Egnatia, which connected northern Italy with Catalonia. Soon, it became an important city, partly because Julius Caesar settled veterans of the Tenth Legion in this city.
A similar story can be told about Arelate, modern Arles: a Roman city in southern France, home to soldiers of Caesar’s Sixth legion Ferrata. Both sites have some ancient monuments left – Arles a bit more than Narbonne, which has a Celtic oppidum across the corner.