structural:summarization
Babylonian rest days

Counting from the new moon, the Babylonians celebrated the 7th, 14th, 21st, and 28th as "holy-days", also called "evil days" (meaning "unsuitable" for prohibited activities). On these days officials were prohibited from various activities and common men were forbidden to "make a wish", and at least the 28th was known as a "rest-day". On each of them, offerings were made to a different god and goddess. Tablets from the 6th-century BCE reigns of Cyrus the Great and Cambyses indicate these dates were sometimes approximate. The lunation of 29 or 30 days basically contained three seven-day weeks, and a final week of nine or ten days inclusive, breaking the continuous seven-day cycle. The Babylonians additionally celebrated the 19th as a special "evil day", the "day of anger", because it was roughly the 49th day of the (preceding) month, completing a "week of weeks", also with sacrifices and prohibitions. Difficulties with Friedrich Delitzsch 's origin theory connecting Hebrew Shabbat with the Babylonian lunar cycle include reconciling the differences between an unbroken week and a lunar week, and explaining the absence of texts naming the lunar week as Shabbat in any language. Reconstruction of a broken tablet seems to define the rarely attested Babylonian Akkadian word Sapattu or Sabattu as the full moon: this word is cognate or merged with Hebrew Shabbat, but is monthly rather than weekly. It is regarded as a form of Sumerian sa-bat ("mid-rest"), attested in Akkadian as um nuh libbi ("day of mid-repose"). This conclusion is a contextual restoration of the damaged Enûma Eliš creation mythos, which is read as: "pattu shalt thou then encounter, midly."

The pentecontad calendar, thought to be of Amorite origin, includes a period known to Babylonians as Shappatum. The year is broken down into seven periods of fifty days (made up of seven weeks of seven days, containing seven weekly Sabbaths, and an extra fiftieth day, known as the atzeret), plus an annual supplement of fifteen or sixteen days, called Shappatum, the period of harvest time at the end of each year. Identified and reconstructed by Hildegaard and Julius Lewy in the 1940s, the calendar's use dates back to at least the 3rd millennium BCE in Western Mesopotamia and surrounding areas; it was used by the Canaanite tribes, thought by some to have been used by the Israelites prior to King Solomon, and related to the liturgical calendar of the Essenes at Qumran. Used well into the modern age, forms of it have been found in Nestorianism and among the Palestinian fellaheen. Julius Morgenstern believed that the calendar of the Jubilees had ancient origins as a somewhat modified survival of the pentecontad calendar.