Alexander appears to have risen in the ranks - though the details are unknown, until, with the reign of Nero, he served as a staff officer under the prominent general Gnaeus Domitius Corbulo during campaigns against Parthia, under whom he distinguished himself. In 63 he was dispatched along with Corbulo's son-in-law to escort the Armenian king Tiridates, with whom he himself had initiated negotiations, to the Roman camp, on the first stage of his journey to receive the status of client king from Nero.