that Crassus and Pompey intensely disliked one another. In 53 BC, Crassus launched a Roman invasion of the Parthian Empire. After initial successes, he marched his army deep into the desert; but here his army was cut off deep in enemy territory, surrounded and slaughtered at the Battle of Carrhae in "the greatest Roman defeat since Hannibal" in which Crassus himself perished. The death of Crassus removed some of the balance in the Triumvirate and, consequently, Caesar and Pompey began to move apart. While Caesar was fighting against Vercingetorix in Gaul, Pompey proceeded with a legislative agenda for Rome that revealed that he was at best ambivalent towards Caesar and perhaps now covertly allied with Caesar's political enemies. In 51 BC, some Roman senators demanded that Caesar would not be permitted to stand for Consul unless he turned over control of his armies to the state, and the same demands were made of Pompey by other factions. Relinquishing his army would leave Caesar defenceless before his enemies. Caesar chose Civil War over laying down his command and facing trial. The triumvirate was shattered and conflict was inevitable. Pompey initially assured Rome and the senate that he could defeat Caesar in battle should he march on Rome. However, by the spring of 49 BC, when Caesar crossed the Rubicon river with his invading forces and swept down the Italian peninsula towards Rome, Pompey ordered the abandonment of Rome. Caesar's army was still under-strength, with certain units remaining in Gaul, but on the other hand Pompey himself only had a small force at his command, and that with uncertain loyalty having served under Caesar. Tom Holland attributes Pompey's willingness to abandon Rome to waves of panicking refugees as an attempt to stir ancestral fears of invasions from the north. Pompey's forces retreated south towards Brundisium, and then fled to Greece. Caesar first directed his attention to the Pompeian stronghold of Iberia but following campaigning by Caesar in the Siege of Massilia and Battle of Ilerda he decided to attack Pompey in Greece. Pompey initially defeated Caesar at the Battle of Dyrrachium in 48 BC but failed to follow up on the victory. Pompey was decisively defeated in the Battle of Pharsalus in 48 BC despite outnumbering Caesar's forces two to one. Pompey fled again, this time to Egypt, where he was murdered in an attempt to ingratiate the country with Caesar and