Achillas subsequently joined Pothinus in resisting Caesar, and having had the command of the whole army entrusted to him by Pothinus, he marched against Alexandria with 20,000 on foot and 2,000 cavalry. Caesar, who was at Alexandria, did not have sufficient forces to oppose him, and sent ambassadors to negotiate with him. However, Achillas murdered the ambassadors to remove all hopes of reconciliation. He then marched into Alexandria and occupied most of the city (Siege of Alexandria (47 BC)). Meanwhile, Arsinoe, the younger sister of Ptolemy, escaped from Caesar and joined Achillas. However, in 47, dissension broke out between them, so Arsinoe had Achillas put to death by Ganymedes, a eunuch to whom she then entrusted the command of the forces.