[7][8] Gaius Cassius Longinus came from a very old Roman family, gens Cassia, which had been prominent in Rome since the 6th century BC.

Cassius led the remaining troops' retreat back into Syria, and organised an effective defence force for the province.

[12] In 51 BC, Cassius was able to ambush and defeat an invading Parthian army under the command of prince Pacorus and general Osaces.

As they set about their return journey they were confronted by a detachment of Cassius' army, which faked a retreat and lured the Parthians into an ambush.

News of Pompey's defeat at the Battle of Pharsalus caused Cassius to head for the Hellespont, with hopes of allying with the king of Pontus, Pharnaces II.

[17] Although Cassius was "the moving spirit" in the plot against Caesar, winning over the chief assassins to the cause of tyrannicide, Brutus became their leader.

In letters written during 44 BC, Cicero frequently complains that Rome was still subjected to tyranny, because the "Liberators" had failed to kill Antony.

[20] Cassius' reputation in the East made it easy to amass an army from other governors in the area, and by 43 BC, he was ready to take on Publius Cornelius Dolabella with 12 legions.

Gaius Julius Caesar Octavian (later known as Augustus) and Mark Antony soon arrived, and Cassius planned to starve them out through the use of their superior position in the country.

Cassius, however, was defeated and overrun by Mark Antony and, unaware of Brutus' victory, ordered his freeman Pindarus to help him kill himself.

"[22] Like Brutus, whose Stoic proclivities are widely assumed but who is more accurately described as an Antiochean Platonist, Cassius exercised a long and serious interest in philosophy.

Although Epicurus advocated a withdrawal from politics, at Rome his philosophy was made to accommodate the careers of many prominent men in public life, among them Caesar's father-in-law, Calpurnius Piso Caesoninus.

[25] Arnaldo Momigliano called Cassius' conversion a "conspicuous date in the history of Roman Epicureanism," a choice made not to enjoy the pleasures of the Garden, but to provide a philosophical justification for assassinating a tyrant.

[26] Cicero associates Cassius's new Epicureanism with a willingness to seek peace in the aftermath of the civil war between Caesar and Pompeius.

[27] Miriam Griffin dates his conversion to as early as 48 BC, after he had fought on the side of Pompeius at the Battle of Pharsalus but decided to come home instead of joining the last holdouts of the civil war in Africa.

The Roman concept of libertas had been integrated into Greek philosophical studies, and though Epicurus' theory of the political governance admitted various forms of government based on consent, including but not limited to democracy, a tyrannical state was regarded by Roman Epicureans as incompatible with the highest good of pleasure, defined as freedom from pain.

[37] The inconsistencies between traditional Epicureanism and an active approach to securing freedom ultimately could not be resolved, and during the Empire, the philosophy of political opposition tended to be Stoic.

This circumstance, Momigliano argues, helps explain why historians of the Imperial era found Cassius more difficult to understand than Brutus, and less admirable.

[33] In Dante's Inferno (Canto XXXIV), Cassius is one of three people deemed sinful enough to be chewed in one of the three mouths of Satan, in the very centre of Hell, for all eternity, as a punishment for killing Julius Caesar.