Lucius Domitius Ahenobarbus had become proconsul of Gaul and was sent to gain control of Massilia (modern Marseille) in order to oppose Caesar. As Caesar marched to Hispania (enroute to confront Pompey's legions), the Massiliots closed their gates to him, having allied with Ahenobarbus and the Optimates. Roused by their hostile actions, he commenced a siege against Massilia, leaving the newly raised XVII, XVIII, and XIX legions to conduct the siege under the command of Gaius Trebonius. He also placed Decimus Brutus in charge of his fleet there. Caesar himself marched with his veteran legions to Hispania to fight the Pompeian generals Lucius Afranius and Marcus Petreius. He would return to the siege of Massilia after defeating his opponents at the battle of Ilerda.