According to Lampridius (Hist. August. p. 135), Alexander Severus lived twenty-nine years, three months, and seven days. As he was killed March 19, 235, he was born December 12, 205, and was consequently about this time thirteen years old, as his elder cousin might be about seventeen. This computation suits much better the history of the young princes, than that of Herodian (1. v. p. 181), who represents them as three years younger; whilst, by an opposite error of chronology, he lengthens the reign of Elagabalus two years beyond its real duration. For the particulars of the conspiracy, see Dion, 1. lxxviii. p. 1339. Herodian, 1. v. p. 184.