Zenobia initially avoided provoking Rome by claiming for herself and her son the titles, inherited from Odaenathus, of subject of Rome and protector of its eastern frontier. After expanding her territory, she seems to have tried to be recognized as an imperial partner in the eastern half of the empire and presented her son as subordinate to the emperor. In late 270, Zenobia minted coinage bearing the portraits of Aurelian and Vaballathus; Aurelian was titled "emperor", and Vaballathus "king". The regnal year in early samples of the coinage was only Aurelian's. By March 271, despite indicating Aurelian as the paramount monarch by naming him first in the dating formulae, the coinage also began bearing Vaballathus' regnal year. By indicating in the coinage that Vaballathus' reign began in 267 (three years before the emperor's), Vaballathus appeared to be Aurelian's senior colleague.