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it-1 pp. 447-448 Chronology
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Eras.
Accurate chronology requires that some point in the stream of time be set as the marker from which to count either forward or backward in time units (such as hours, days, months, years). That starting point could be simply the sunrise (for measuring the hours of a day), or a new moon (for measuring the days of a month), or the start of the spring season (for measuring the span of a year). For counting longer periods, men have resorted to the establishing of a particular “era,” using some outstanding event as their starting point from which to measure periods of many years. Thus, in nations of Christendom, when a person says that ‘today is October 1, 1987 C.E. (Common Era),’ he means that ‘today is the first day of the tenth month of the one thousand nine hundred and eighty-seventh year counting from what was believed by some to be the time of the birth of Jesus.’
Such use of an era in secular history is of rather late inception. The Greek era, supposedly the earliest secular case of such chronological reckoning, apparently was not put into practice until about the fourth century B.C.E. (Before the Common Era). The Greeks figured time by means of four-year periods called Olympiads, starting from the first Olympiad, calculated as beginning in 776 B.C.E. Additionally, they often identified specific years by referring to the term of office of some particular official. The Romans eventually established an era, reckoning the years from the traditional date of the founding of the city of Rome (753 B.C.E.). They also designated specific years by reference to the names of two consuls holding office in that year. It was not until the sixth century C.E. that a monk named Dionysius Exiguus calculated what is now popularly known as the Christian Era, or, more correctly, the Common Era. Among the Muhammadan (Islamic) peoples the years are dated from the Hegira (Muhammad’s flight from Mecca in 622 C.E.). The early Egyptians, Assyrians, and Babylonians, however, give no evidence of having used such an era system consistently over any considerable period of time.
