Seleucid Era

The Seleucid era or Anno Graecorum (literally "year of the Greeks" or "Greek year"), sometimes denoted "AG", was a system of numbering years in use by the Seleucid Empire and other countries among the ancient Hellenistic civilizations. The era dates from the return of Seleucus I Nicator to Babylon in 311 BC after his exile in Ptolemaic Egypt, considered by Seleucus and his court to mark the founding of the Seleucid Empire. The introduction of the new era is mentioned in one of the Babylonian Chronicles, the Chronicle of the Diadochi.

Two different uses were made of the Seleucid years:

1. The natives of the empire used the Babylonian calendar, in which the new year falls on 1 Nisanu (3 April in 311 BC), so in this system year 1 of the Seleucid era corresponds roughly to April 311 BC to March 310 BC. This included the Jews, who call it the Era of Contracts. It is used in the Jewish historical book, now "deuterocanonical", 1 Maccabees, in 6:20, 7:1, 9:3, 10:1, etc.
2. The Macedonian court adopted the Babylonian calendar (substituting the Macedonian month names) but reckoned the new year to be in the autumn (the exact date is unknown). In this system year 1 of the Seleucid era corresponds to the period from autumn 312 BC to summer 311 BC. By the seventh century AD / tenth AG, the west Syrian Christians settled on 1 October-to-30 September.

These differences in the beginning of the year mean that dates may differ by one. Bickerman gives this example:

For instance, the restoration of the temple of Jerusalem by Judas Maccabaeus, approximately 15 December 164 BC, fell in the year 148 of the Seleucid Era according to Jewish (and Babylonian) calculation, but in the year 149 for the court.

The Seleucid era was used as late as the 6th century AD, for instance in the Zebed inscription in Syria, dated the 24th of Gorpiaios, 823 (24 September, 512 AD), and in the writings of John of Ephesus. Syriac chroniclers continued to use it up to Michael the Syrian in the 1100s AD / 1400s AG. It has been found on Nestorian Christian tombstones from Central Asia well into the 14th century AD.

The Jewish / Babylonian calendar was used by Yemenite Jews until modern times, and continues to be used by them for certain ritual purposes even today.