TheSeleucid era ("SE") orAnno Graecorum (literally "year of the Greeks" or "Greek year"), sometimes denoted "AG," was asystem of numbering years in use by theSeleucid Empire and other countries among the ancientHellenistic civilizations, and later by theParthians. It is sometimes referred to as "the dominion of the Seleucidæ," or the Year of Alexander. The era dates fromSeleucus I Nicator's reconquest ofBabylon in 312/11 BC after his exile inPtolemaic Egypt,^[1] considered by Seleucus and his court to mark the founding of the Seleucid Empire. According to Jewish tradition, it was during the sixth year ofAlexander the Great's reign (lege: possibly Alexander the Great's infant son,Alexander IV of Macedon) that they began to make use of this counting.^[2]

Two different variations of the Seleucid years existed, one where the year started in spring and another where it starts in autumn:

1. The natives of the empire used theBabylonian 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 inhabitants ofCoele-Syria, notably the Jews who call it theEra of Contracts (Hebrew:מניין שטרות,romanized: minyān shəṭarot).
2. TheMacedonian court adopted the Babylonian calendar (substituting theMacedonian 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 7th century AD / 10th AG, the west Syrian Christians settled on 1 October-to-30 September.^[3] Jews, however, reckon the start of each new Seleucid year with the lunar monthTishri.^[4]

These differences in the beginning of the year means that dates differ by one if they fall between spring and autumn. Notably, the Jewish historical book1 Maccabees generally uses the Babylonian and Judean year count (1 Maccabees 6:20,1 Maccabees 7:1, 9:3, 10:1, etc.).^[5] However, the book2 Maccabees exclusively uses the Macedonian version of the calendar, likely because it was written in either Cyprus or Egypt.^[6]Elias Bickerman gives this example:

For instance, the restoration of the temple of Jerusalem byJudas 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.^[7]

The Seleucid era was used as late as the sixth century CE, for instance in theZabad inscription inSyria, dated the 24th ofGorpiaios, 823 (24 September, 512 AD),^[11] and in the writings ofJohn of Ephesus.^[12] Syriac chroniclers continued to use it up toMichael the Syrian in the 12th century AD / 15th century AG.^[3] It has been found onCentral Asian tombstones of Christians belonging to theChurch of the East well into the 14th century AD.^[13]

The Seleucid era counting, or "era of contracts" (minyan shəṭarot), was used byYemenite Jews in their legal deeds and contracts until modern times,^[14] a practice derived from an ancient Jewish teaching in theTalmud, requiring allDiaspora Jews to uphold its practice.^[15] For this reason, the Seleucid era counting is mentioned in theBook of Maccabees (I Macc. i. 11) and in the writings of the historianJosephus. The Seleucid era counting fell into disuse among most Jewish communities, following RabbiDavid ben Zimra's cancellation of the practice when he served as Chief Rabbi of Egypt.^[16]

• Robert Harry van Gent.The Babylonian Calendar. Has a date converter based on Parker & Dubberstein (1971).
• Kosmin, Paul J. (2018).Time and Its Adversaries in the Seleucid Empire.Harvard University Press.ISBN 9780674976931.
• Kosmin, Paul J. (7 May 2019)."A revolution in time".aeon. Retrieved12 January 2020.Once local and irregular, time-keeping became universal and linear in 311 BCE. History would never be the same again.
• Strootman, Rolf (2015)."Seleucid Era".Encyclopaedia Iranica. Leiden: Brill. Retrieved14 May 2021.