Why Do We Have A Seven-Day Week?

The seven-day week has no correspondence to astronomy – unlike the presence of the sun giving us days, or phases of the moon giving us months. Historians generally think the seven-day week was “invented” by Mesopotamians and/or Jews. Both thought the number seven had mystic significance. Sumer had a (mostly) seven-day week system since at least the 21st century BCE. The Jewish weeks may have developed independently or been influenced by their Fertile Crescent neighbors.

From the crossroads of Europe, Asia, and Africa the seven-day week spread around the Old World. The Greeks and Persians adopted the Babylonian system, and fro Persia it spread to India and China in various forms. In Japan, for instance, seven-day weeks were mainly used by specialist astrologers until the 1800s. In Europe, it was officially adopted by the Roman Empire in the 300s CE, but it was already in common use throughout the empire.