The day of the full moon, when the moon is neither increasing nor decreasing, the Babylonians called Sa-bat, meaning "heart-rest." It was believed that on this day, the woman in the moon, Ishtar, as the moon goddess was known in Babylon, was menstruating, for in Babylon, as in virtually every ancient and primitive society, there had been since the earliest times a taboo against a woman working, preparing food, or traveling when she was passing her monthly blood. On Sa-bat, from which comes our Sabbath, men as well as women were commanded to rest, for when the moon menstruated, the taboo was on everyone. Originally (and naturally) observed once a month, the Sabbath was later to be incorporated by the Christians into their Creation myth and made conveniently weekly. So nowadays hard-minded men with hard muscles and hard hats are relieved from their jobs on Sundays because of an archetypal psychological response to menstruation.