For everyone who wants to learn how the calendar came about Dominus Exiguus was the very first to switch over to our current calendar.
Prior, all calendars were dated to Ab Urbe Condita -”from the founding of the City”, ie, Rome.
There’s a discreprency of about 200 years between Ab Urbe Condita and the Jewish Calendars that has yet to be resolved.
Teaching BCE + CE is just bad history! Every history teacher should be taught and teaching that the current system was set up by Dominus Exiguus! That is why it is BC and AD, Before Christ and “Anno Domini”, year of our Lord.