The Romans took the town in 123 BC and expanded it into an important city, with a canal link to the Mediterranean Sea being constructed in 104 BC. However, it struggled to escape the shadow of Massalia (Marseille) further along the coast.
Its chance came when it sided with Julius Caesar against Pompey, providing military support. Massalia backed Pompey; when Caesar emerged victorious, Massalia was stripped of its possessions, which were transferred to Arelate as a reward. The town was formally established as a colony for veterans of the Roman legion Legio VI Ferrata, which had its base there. Its full title as a colony was Colonia Iulia Paterna Arelatensium Sextanorum, “the ancestral Julian colony of Arles of the soldiers of the Sixth.”