Lucius Domitius Ahenobarbus, who had become proconsul of Gaul, is sent in April 49 to gain control of Massalia (modern Marseille) in order to oppose Caesar.

As Caesar marches to Spain (en route to the Battle of Ilerda), the Massiliots close their gates to him, having allied with Ahenobarbus and the Optimates.

Roused by their hostile actions, he commences a siege against Massallia, leaving the newly raised XVII, XVIII, and XIX legions to conduct the siege.

These are the same legions that will be wiped out at Teutoburg Forest fifty-eight years later.

He also places Decimus Junius Brutus Albinus in charge of his fleet here.

After the siege has begun, Ahenobarbus arrives in Massallia to defend it against the Caesarian forces.

In late June, Caesar's ships, although they are less skillfully built than those of the Massiliots and outnumbered, are victorious in the ensuing naval battle, after which the fleet is confiscated by the Roman authorities.

Gaius Trebonius, Caesar's legatus, conducts the siege using a variety of siege machines including siege towers, a siege-ramp, and a "testudo-ram".

Gaius Scribonius Curio, careless in adequately guarding the Sicilian Straits, allows Lucius Nasidius to bring more ships to the aid of Ahenobarbus.

He fights a second naval battle with Decimus Brutus in early September, but withdraws defeated and sails for Spain.

The Massiliots valiantly defend against the siege machines and works.

They throw down burning pitch and pine-shavings as the Caesarians undermine the foundations of their city walls.

At one point they seem likely to surrender and declare a truce, but at night they cunningly destroy the siege works in a gross violation of the treaty.

They are now near surrender.

At the final surrender of Massallia, Caesar shows his usual leniency and Lucius Ahenobarbus escapes to Thessaly in the only vessel that is able to escape from the Populares.

Afterwards, Massallia loses its independence and is absorbed into the Roman Republic.

During Roman times the city is called Massilia.