Gaius Cassius Longinus emerged from the gens Cassia, a family that had held prominence in Rome since the 6th century BC. His early years remain obscure to modern historians, yet one story survives about his youth at school. He quarreled with the son of Lucius Cornelius Sulla, the dictator who had seized control of the Roman state. This childhood conflict signaled an early dislike for despots and set the tone for his future political life. Cassius later studied philosophy under Archelaus of Rhodes, where he became fluent in Greek. He married Junia Tertia, the daughter of Servilia, making him the brother-in-law of Marcus Brutus. They had one son born around 60 BC.
The Retreat From Carrhae
In 54 BC, Gaius Cassius Longinus joined Marcus Licinius Crassus on an eastern campaign against the Parthian Empire as quaestor. The following year, Crassus led the Roman army into Northern-Mesopotamia at the Battle of Carrhae. It stands as the worst defeat since Hannibal destroyed a Roman force at Cannae in 216 BC. Cassius organized the retreat of remaining troops back into Syria and formed an effective defense force for the province. Plutarch suggests that Crassus could have avoided this crushing defeat by listening to Cassius's advice not to invade Parthia. After the disaster, Roman soldiers and even Crassus himself were willing to give overall command to Cassius, but he refused it. Dio records that the Parthians viewed Cassius as equal to Crassus in authority yet superior in ability.