Under Nero, the Romans fought a campaign (55–63) against the Parthian Empire, which had invaded the Kingdom of Armenia, allied with the Romans. After gaining Armenia in 60, then losing it in 62, the Romans sent the Legio XV "Apollinaris" from Pannonia to Gnaeus Domitius Corbulo, "legatus" of Syria. In 63, strengthened further by the legions III "Gallica", V "Macedonica", X "Fretensis" and XXII, General Corbulo entered into the territories of Vologases I of Parthia, who then returned the Armenian kingdom to Tiridates, king Vologases I's brother.