The "cursus honorum" of Celsus has been recorded in a Latin inscription recovered at Ephesus. According to it, his earliest recorded office was military tribune in Legio III Cyrenaica, which was part of the garrison of Roman Egypt. The next recorded event in his life was his adlection into the Senate "inter aedilicios" by Vespasian and his son Titus, which was a reward Vespasian is known to have made to individuals who supported him during the Year of the Four Emperors. Exactly how Celsus supported Vespasian is not known: the governor of Egypt at the time, Tiberius Julius Alexander, was the first governor to declare publicly for Vespasian (1 July 69); a vexillation of Legio III Cyrenaica participated in the Jewish War and Celsus may have come to Vespasian's notice that way. Regardless of the reason, promotion to the Senate was a significant social and political achievement for Celsus.