Babylonian calendar

The Babylonian calendar was a lunisolar calendar with years consisting of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset, plus an intercalary month inserted as needed by decree. The calendar is based on a Sumerian (Ur III) predecessor preserved in the Umma calendar of Shulgi (c. 21st century BC).

Months

The year begins in spring, and is divided into reš šatti "beginning", mišil šatti "middle", and kīt šatti "end of the year". The word for "month" was arḫu (status constructus araḫ). That the calendar originates in Babylonian, and not in later Assyrian times is shown by the fact that the chief deity of the Assyrians is assigned the surplus intercalary month. During the 6th century BC Babylonian exile of the Hebrews, the Babylonian month names were adopted into the Hebrew calendar. The Assyrian calendar used in Iraq and the Levant also uses many of the same names for its months, such as Iyyar, Tammuz, Ab, Elul, Tishri, and Adar.