Julius Gaius Caesar was committing treason against the Roman Republic when he crossed this river.
The Tiber
The Isonzo
The Rubicon
The Po
The Rubicon. Caesar crossed the Rubicon in 49 BC to march on Rome – he was now irrevocably at war with the Republic and Pompey the Great. The Senate and Pompey fled to Greece, where they consolidated Pompey’s army and awaited Caesar’s attack. He eventually beat the Republic at the battles of Pharsalus, Dyrrhachium, and Munda. After the civil war Caesar became Perpetual Dictator of Rome, leading to the Roman Empire.