According to Jerome’s Chron., Theonas became bishop in the sixth year of Probus (281 a.d.); according to the Armenian, in the first year of Numerian and Carinus, i.e. a year later. Both agree with the History in assigning nineteen years to his episcopate. An interesting and admirable epistle is extant addressed to Lucian, the chief chamberlain of the emperor, and containing advice in regard to the duties of his position, which is commonly and without doubt correctly ascribed to Theonas. The name of the emperor is not given, but all of the circumstances point to Diocletian, who had a number of Christians in influential positions in his household during the earlier years of his reign. The epistle, which is in Latin (according to some a translation of a Greek original), is given by Routh, Rel. Sac. III. 439–445, and an English translation is contained in the Ante-Nicene Fathers, VI. p. 158–161.