Massalia is one of those other places that the AI (especially the romans) go crazy for. In my most recent Arverni campaign, a regular tribute of 100 mnai for X turns (constantly renewed) has kept me at peace with the Romans since 270BC (it's 215BC now). The romans instead directed their attention eastwards and wasted fullstack after fullstack trying to take Mrogbonna, without success.

Same thing in my koinon campaign, a regular tribute has kept the pontic princes away from Byzantion for 40 years and are now on a killing spree in the east, effectively dividing the world into two spheres of interests.

Early alliances + regular tributes is the key.