AR24 - Antoninus Pius L ΔωΔΕΚΑΤΟΥ

The dating formula ΔωΔΕΚΑΤΟΥ — "of the twelfth year" — places this issue in Antoninus Pius's twelfth regnal year by Egyptian reckoning, a calendar system the Alexandrian mint maintained independently of the Roman consular dating used elsewhere in the empire. Alexandria's billon tetradrachms from this period are among the better-documented provincial issues, with die studies by Emmett and others allowing reasonably precise sequencing within a given regnal year. The metal itself was already debased well before this reign; the mint had been running billon rather than true silver since at least the Neronian reforms of the 60s AD.