Gaius Cassius Longinus emerged from the gens Cassia, a family that had held prominence in Rome since the 6th century BC. He studied philosophy under Archelaus of Rhodes and became fluent in Greek.
Cassius organized the retreat of remaining troops back into Syria and formed an effective defense force for the province after Crassus led the Roman army into Northern-Mesopotamia. Plutarch suggests that Crassus could have avoided this crushing defeat by listening to Cassius's advice not to invade Parthia.
The decisive encounter occurred on October 7 as the Parthians turned away from Antigonea during their return journey. A detachment of Cassius's army faked a retreat to lure the enemy into an ambush where they were surrounded and defeated by Cassius's main forces.
Although Cassius was the moving spirit behind the plot, he felt deeply offended when his junior and brother-in-law Marcus Brutus received the appointment as praetor urbanus instead of himself. On the Ides of March, 44 BC, Cassius urged fellow liberators on and struck Caesar in the chest.
Cassius was defeated and overrun by Mark Antony while unaware that Brutus had successfully defeated Octavian. He ordered his freeman Pindarus to help him kill himself before his head was found severed from his body.