Quintus Labienus Parthicus (died 39 BC), the son of
Titus Labienus, was a Roman republican general, later in the service of
Parthia. After the then main political power in Rome,
Julius Caesar, was murdered by a conspiracy in 44 BC, Labienus took the side of the pro-republic conspirators, led by
Brutus and
Cassius, the latter of whom he served in the capacity of an ambassador to the Parthians. After Brutus and Cassius fled east to Macedonia and were defeated there in the
Battle of Philippi by Caesar's imperialist successors (the
Second Triumvirate, particularly
Mark Antony and Caesar's heir Octavian, the future emperor
Augustus), Labienus joined the Parthians. The Parthians invaded the Roman territories in 40 BC, led by
Pacorus and Labienus. The Parthian army crossed the
Euphrates and attacked
Apamea. The attack on Apamea failed but Labienus was able to entice the Roman garrisons around Syria to rally to his cause. The combined Romano-Parthian army then proceeded to defeat
Mark Antony's governor
L. Decidius Saxa in a pitched battle and took Apamea. After the Roman defeat at Apamea, the Parthians split their army. Pacorus turned south and conquered the Levant from the Phoenician coast through Palestine. Labienus turned north to follow Saxa, whom he defeated and killed in
Cilicia.