The Reckoning by the Regnal Years and Victories of Valerian and Gallienus

The statement of L. Wickert that the numbers of the tribuniciae potestates of Gallienus (and of Valerian) are contradictory and also in part evidently wrong can also be applied to the numbering of the consulates of those rulers. There are, however, two kinds of discrepancy in the reckoning of imperial years in this period, caused respectively by ordinary blunders and by abnormal methods of numbering. As the latter kind of discrepancy does not alter the relative exactness of the chronology, abnormal reckoning has, rightly interpreted, the same documentary value as the strictly correct system. Inscriptions, of course, do not offer opportunities of discriminating between occasional mistakes and incorrect systems as the cause of error, but the character of erroneous reckonings can be discerned on coins through continuity of reckoning in successive years in any given mint.