How did the Jews calculate the starting year -3761 of their calendar?

Answer

There are many different starting points for an era in Jewish culture, very often the beginning of a king’s reign, the start of a dynasty or the Babylonian captivity. Compare it with the Romans, who also counted from the mythical foundation of Rome (Ab Urbe Condita). The most commonly used era in the period 200 BC-600 AD. was the Seleucid era, which around 312-311 BC. laid a starting point with the foundation of the Seleucid (Babylonian dynasty). That count is used in 1 Maccabees, among others. Yemeni Jews used the Seleucid count as late as the 20th century.

The count you refer to is called the Anno Mundi era, counted ‘from creation’. In 1178 AD. Maimonides wrote in his Mishneh Torah how, using ancient scriptures, he had calculated the moment of the creation of the world (by the way, creation fell in the last week of that year 1). At the same time, he also gave guidelines to make the calendar more precise. Maimonides’ calendar system and Anno Mundi starting point have been used as the Jewish era ever since. Maimonides, however, was not the first scribe to attempt to calculate the date of creation. The Seder Olam Rabbah from 160 AD. of Rabbi Jose ben Halafta was one long chronological listing that ended up at 3761 BC. as a starting point. And the Byzantine calendar, using the Septuagint version of the Book of Genesis, came out at 5509 BC, 1732 years earlier…