<P> A continuous seven - day cycle that runs throughout history paying no attention whatsoever to the phases of the moon was probably first practiced in Judaism, dated to the 6th century BC at the latest . </P> <P> There are several hypotheses concerning the origin of the biblical seven - day cycle . </P> <P> Friedrich Delitzsch and others suggested that the seven - day week being approximately a quarter of a lunation is the implicit astronomical origin of the seven - day week, and indeed the Babylonian calendar used intercalary days to synchronize the last week of a month with the new moon . According to this theory, the Jewish week was adopted from the Babylonians while removing the moon - dependency . </P> <P> However, Niels - Erik Andreasen, Jeffrey H. Tigay and others claimed that the sabbath is mentioned as a day of rest in some of the earliest layers of the Pentateuch dated to the 9th century BC at the latest, centuries before Judea's Babylonian exile . They also find the resemblance between the biblical Sabbath and the Babylonian system weak . Therefore they suggested that the seven - day week may reflect an independent Israelite tradition . Tigay writes: </P>

Where did the 7 days of the week come from