Under Nero, the Romans fought a campaign (55–63) against the Parthian Empire, which had invaded the kingdom of Armenia, allied to the Romans. After gaining Armenia in 60 and losing it in 62, the Romans sent XV "Apollinaris" from Pannonia to Cn. Domitius Corbulo, "legatus" of Syria. Corbulo, with the legions XV "Apollinaris", III "Gallica", V "Macedonica", X "Fretensis" and XXII, forced Vologases I of Parthia to a compromise peace in 63, whereby his brother Tiridates would become king of Armenia as a Roman client.