Caracalla's father appointed Caracalla joint "augustus" and full emperor from 28 January 198. This was the day of Septimius Severus's triumph was celebrated, in honour of his victory over the Parthian Empire in the Roman–Persian Wars; he had successfully sacked the Parthian capital, Ctesiphon, after winning the Battle of Ctesiphon, probably in October 197. He was also awarded tribunician power and the title of "imperator". In inscriptions, Caracalla is given from 198 the title of the chief priesthood, "pontifex maximus". His brother Geta was proclaimed "nobilissimus caesar" on the same day, and their father Septimius Severus was awarded the victory name "Parthicus Maximus".