After the institution of the Roman Empire, regnal dates based on the emperors’ terms in office became more common. Some historians of the later republic and early imperial eras dated from the legendary founding of the city of Rome (ab urbe condita or AVC).[32]
So it’d be more like the ninth year of the reign of Emperor Tiberius.
They would have written XXIII.
Pretty sure that at that point, they weren’t dating things off Christ’s birth.
looks
https://en.wikipedia.org/wiki/Roman_calendar
So it’d be more like the ninth year of the reign of Emperor Tiberius.