As the previous commenter said, the Consuls elected for that year, or the number of years since Rome founded (AUC - ‘Ab Urbe Condita’), or, in the period of the Roman Empire, the year of the reigning Emperor (ie “in the third year of our beloved Emperor Tiberius”)
As the previous commenter said, the Consuls elected for that year, or the number of years since Rome founded (AUC - ‘Ab Urbe Condita’), or, in the period of the Roman Empire, the year of the reigning Emperor (ie “in the third year of our beloved Emperor Tiberius”)