In 34 BCE, the Roman commander Mark Antony had invaded Armenia and had captured king Artavasdes II and some of his relatives. It was Antony's ambition to put a son of the Ptolemaic queen, the famous Cleopatra VII Eupator, and himself, Alexander Helios, on the Armenian throne, but Antony's defeat at Actium prevented this plan. In 31/30, Artavasdes was executed, and in Armenia, Artaxias II became king, supported by the Parthians.
Meanwhile, Artavasdes' relatives had been brought to Rome, where the new leader, the emperor Augustus (r.27 BCE - 14 CE) kept them in detention. One of these people was Artavasdes' brother Tigranes. When in the year 20 BCE pro-Roman Armenians killed king Artaxias II, Augustus proclaimed Tigranes king of Armenia. Augustus' stepson Tiberius and Archelaus of Cappadocia saw to Tigranes' accession.note[Augustus, Res Gestae 27; Josephus, Jewish Antiquities 15.104; Tacitus, Annals 2.3.]
Tiberius also concluded a deal with the Parthian king Phraates, in which the two parties agreed that Armenia was to be independent but that the Romans had the right to appoint and crown the kings. This treaty was to be in force for more than seventy years.
Tigranes III was succeeded by his son Tigranes IV.