The chronology of Ammianus is loose and obscure; and Orosius (1. vii. c. 33, p. 551, edit. Havercamp.) seems to place the revolt of Firmus after the deaths of Valentinian and Valens. Tillemont (Hist. des Emp. tom. v. p. 691) endeavours to pick his way. The patient and sure-footed mule of the Alps may be trusted in the most slippery paths.