By the mid-2nd century BC, Rome was trading heavily with the Greek colony of Massalia (modern Marseille) on the southern coast of Gaul. Massalia, founded by colonists from Phocaea, was by this point centuries old and quite prosperous. Rome entered into an alliance with Massalia, by which it agreed to protect the town from local Gauls, nearby Aquitani, sea-borne Carthaginians and other rivals, in exchange for a small strip of land that it wanted in order to build a road to Hispania, to assist in troop transport.
Source: Gallia Narbonensis – Wikipedia
Tim B.
“In this strip of land, the Romans founded the town of Narbonne in 118 BC. At the same time, they built the Via Domitia, the first Roman road in Gaul, connecting Gaul to Hispania, and the Via Aquitania, which led toward the Atlantic through Tolosa (Toulouse) and Burdigala (Bordeaux). Thus the Romans built a crossroads that made Narbonne an optimal trading center, and Narbonne became a major trading competitor to Massalia. From Narbonne, the Romans established the province of Transalpine Gaul, later called Gallia Narbonensis. “