The Beginning of the Common Era

This mark on the timeline is not an event within Jewish history but the zero point of another calendar that eventually became the world's. In the sixth century the monk Dionysius Exiguus proposed counting years from the presumed birth of Jesus of Nazareth rather than from a Roman emperor's accession. That date fell in the year 3760 from Creation by the reckoning of Seder Olam. Hence the practical rule still in use: subtract 3760 from the year of Creation to get the Gregorian year—3761 for events after the autumn Rosh Hashanah.

The era in question was one of extreme tension in Judea. Herod was dead, the country divided among his sons, then placed under direct Roman prefects. Preachers, healers and self-declared emissaries moved through the land; Josephus lists several such movements, each ending in dispersal or execution. The sages of that generation—Rabban Gamliel the Elder, Hillel's grandson, and his contemporaries—were occupied with something else: preserving the law in a country where the Roman governor appointed High Priests at will.

For this timeline the point is arithmetic: from here two systems of counting run in parallel.

The Christian era is counted from a date calculated in the sixth century by Dionysius Exiguus, and that calculation is itself acknowledged to be mistaken: by the Gospel reference to the reign of Herod, who died in 4 BCE, the event from which the count runs falls several years before the era's zero point.