Quintus Labienus, a Roman republican general, following Caesar’s murder had taken the side of Brutus and Cassius, the latter whom he had served in the capacity of an ambassador to the Parthians.
After Brutus and Cassius were defeated at Philippi, Labienus had joined the Parthians, who invade the Roman territories in 40 BCE.
The Parthian army, led by Labienus and their king, Pacorus, crosses the Euphrates and attacks Apamea.
The attack on Apamea fails but Labienus is able to entice the Roman garrisons around Syria to rally to his cause.
The combined Romano-Parthian army then proceeds to defeat Mark Antony's governor L. Decidius Saxa in a pitched battle and takes Apamea.
After the Roman defeat at Apamea, the Parthians split their army.
Pacorus turns south and conquers the Levant from the Phoenician coast through Palestine, with the exception of a few cities that hold out, including Tyre.
Labienus turns north to follow Saxa, who loses most of his troops as he retreats to Antioch, and whom Labienus defeats and kills in Cilicia.
Labienus then proceeds to conquer all of Asia Minor.
Under Labienus and Pacorus, the Parthians have restored their territory to nearly the limits of the old Achaemenid empire and control all of Asia Minor except for a few cities.
The Parthian successes are not to be long-lasting, however.
