The seven day cycle ultimately replaced the older Roman system of the nundinal cycle, probably during the 4th century.
The earliest evidence of an astrological significance of a seven-day period is connected to Gudea, priest-king of Lagash in Sumer during the Gutian dynasty, who built a seven-room temple, which he dedicated with a seven-day festival.
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".
The forerunner of all modern Zoroastrian calendars is the system used to reckon dates in the Persian Empire, adopted from the Babylonian calendar by the 4th century BC. Senn in his book Christian Liturgy: Catholic and Evangelical points to data suggesting evidence of an early continuous use of a seven-day week; referring to the Jews during the Babylonian Captivity in the 6th century BC, after the destruction of the Temple of Solomon.
They also find the resemblance between the biblical Sabbath and the Babylonian system weak.