His actions alienated the Armenians and also some of his nobles, including the distinguished Monaeses, who fled to the Roman triumvir Mark Antony, but shortly returned and reconciled with Phraates IV.

Phraates IV was attacked in 36 BC by Mark Antony, who marched through Armenia into Media Atropatene, and was defeated and lost the greater part of his army.

But when the war with Octavian broke out, Antony could not maintain his conquests; Phraates IV recovered Media Atropatene and made Artaxias, the son of Artavasdes II, king of Armenia.

Around the same time, Phraates IV's throne was usurped by Tiridates II, but he quickly managed to reestablish his rule with the aid of Scythian nomads.

[4] Fearing that his position might become endangered, Phraates IV executed all his half-brothers–the sons of Orodes and his Commagenian wife Laodice, partially due to their maternal descent being greater than that of his own.

[6] Phraates IV also had supporters of his brothers and his own opponents sent into exile; one of them, Monaeses, a Parthian nobleman who had distinguished himself as a military leader under Orodes II, fled to Syria, where he took refuge with the Roman triumvir Mark Antony.

[8][9] Around the same time, Antony had restored Roman rule in Jerusalem, and executed the Parthian puppet king Antigonus II Mattathias, who was succeeded by Herod the Great.

Antony invaded Media Atropatene, then ruled by Parthia's ally Artavasdes I, with the intention of seizing the capital Praaspa, the location of which is now unknown.

He was taken captive in 34 BC, paraded in Antony's mock Roman triumph in Alexandria, Egypt,[14] and eventually executed by Cleopatra VII of the Ptolemaic Kingdom.

[19] Around this time, Tiridates II of Parthia briefly overthrew Phraates IV, who was able to quickly reestablish his rule with the aid of Scythian nomads.

[24] Emma Strugnell (2008) has suggested that Augustus' choice to send Musa may have been an attempt to obtain information or influence the Parthian king to the advantage of the Romans.

[30] Under Phraates IV and his father, the production of coins reached its zenith, with the only Parthian ruler having similar numbers being Mithridates II (r. 124–88 BC).

[32][33] In the Parthian era, Iranians used Hellenistic iconography to portray their divine figures,[36][37] thus the investiture scene can be associated with the khvarenah, with Tyche being either a representation of Anahita or Ashi.