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 avoid a war with Rome.