The death of Crassus ended the Triumvirate, and left Caesar and Pompey facing each other; their relationship had already degraded after the death of Julia in 54 BC. Pompey then sided with the Optimates, the conservative faction opposed to the Populares—supported by Caesar—and actively fought Caesar in the senate. In 49 BC, with the conquest of Gaul complete, Caesar refused to release his legions and instead invaded Italy from the north by crossing the Rubicon with his army. The following civil war eventually led to Caesar's victory over Pompey at the Battle of Pharsalus in 48 BC and the latter's assassination in Ptolemaic Egypt where he fled after the battle. In 44 BC Caesar was assassinated in Rome and the following year his adopted son Octavian (later known as Augustus) formed the Second Triumvirate with Mark Antony and Marcus Aemilius Lepidus.