Olympiads, the ancient Greek era of four-year periods between Olympic Games, beginning in 776 BC. Ab urbe condita (753 BC), used in the Roman imperial period. The Anno Domini or "Common Era" era, still in use with the Gregorian and Julian calendars today, marks the Incarnation of Jesus as calculated in the 6th century by Dionysius Exiguus.[1] Anno Mundi (years since the creation of the world) as used in the Byzantine calendar (5509 BC).