Historically, Ancient Massilia was founded in 600 B.C. by greeks from Asia Minor. The city became a major sea-power, but was eventually conquered in 125 B.C. under pressure from the Gauls and Romans.
In the game, you control Massilia and Narbo Martius, and are at war with the Gauls and Rome. You have one small fleet (sorry, didn't really have time to make ships...hoplites and peltasts had a priority with the huge Gaulic armies that were constantly attacking) and 2 small armies (they may be small, but they can still hold the bridges around Massilia). The game is on VH/VH, and the goal is to survive as long as the real Massilians did.
Will you make it that long? Or will you greatly surpass the real leaders? You have many paths to choose from, and the fate of this out-post of Greek-civilization on the barbarian frontier depends on the one you choose.