Calendar eras which are, or have been, in use.
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“Ab urbe condita (related with Anno Urbis Conditae: AUC or a.u.c. or a.u.) is Latin for "from the...Ab urbe condita
“Common Era (also Current Era or Christian Era), abbreviated as CE, is an alternative designation...Common Era
“Astronomical year numbering is based on AD/CE year numbering, but follows normal decimal integer...Astronomical year numbering