The reckoning of time in the ancient world differed in many important aspects from the habits familiar to us in the modern word. Whereas we label the years with a number counting the years from the birth of Jesus Christ, and hence attach great importance to the new millennium, the custom of the ancient Greeks and Romans was to label the years with the name or names of particular officials who held office in that year. This greatly complicated the designation of a year in a manner which would be familiar to the people of more than a single city. The labeling of years according to Olympiads, which was developed by historians in the Hellenistic period, was never used much for dating contemporary official documents. Moreover, the calendars of ancient Greek cities, unlike the modern calendar descended from the Roman calendar, were flexible: it was possible to insert εμβόλιμοι days into them to postpone a festival, and afterwards suppress the same number of days to bring the calendar back into order.