The Pompeian–Parthian invasion of 40 BC occurred after the Pompeians, backed by the Parthian Empire, had been defeated during the Liberators' civil war by Mark Antony and Octavian.

King Orodes II sent a Parthian force under Prince Pacorus I and Pompeian General Quintus Labienus in 40 BC to invade the eastern Roman territories while Antony was in Egypt.

Roman soldiers in Syria, many of whom had fought against Caesar during the last civil war, joined the force, and the Levant and much of Asia Minor were swiftly overrun by respectively Pacorus I and Labienus.

[3] In 42 BC, Parthian forces fought against the Caesarians under Mark Antony and Octavian in the Battle of Philippi during the Liberators' civil war.

After the defeat of the Liberators, who had assassinated Caesar, Quintus Labienus, a general who attempted to resurrect the Pompeian cause and had been sent to Parthia to ask for assistance in the last civil war, joined the Parthians.

[2] Pacorus I had gained a reputation for military talent and moderation and swiftly took all the cities along the Levantine coast with the exception of Tyre, which was notoriously difficult to capture.

[8] In 38 BC, Mark Antony finally began his campaign against Parthia with a large force, but it resulted in a defeat with heavy Roman losses.