According to Plutarch, Mithridates was an ally of the Roman triumvir Mark Antony. In 31 BC, Mithridates personally led his forces to Actium in Greece in support of Antony in the war against Caesar Octavian, the future Roman emperor Augustus. After the defeat of Antony, however, Mithridates became a loyal ally to Augustus. Nevertheless, Augustus forced Mithridates to hand over a village in Commagene called Zeugma, which was a major crossing point of the Euphrates River, to the Roman province of Syria. To show his support for Augustus, Mithridates dropped the title "Philhellen" ("friend of the Greeks") from his Aulic titulature and adopted the title "Philorhomaeus" ("friend of the Romans") instead. Both titles were derived from the Commagenean royal cult that Mithridates' father had founded, and in which Mithridates played an important role. His other title "Monocrites" is an otherwise unattested title and was most likely a judicial function within the royal administration and a sign of his high social standing.