Known as an interval between Market Days. In central Asia five days was used, Egyptians used ten days and the Babylonians like the multiple of seven because of the lunations of the moon. In Rome the eight day cycle was used for market. The origin of the seven day week seems to be related to the four (about) seven day phases of the moon. Also the seven colors in the rainbow, and in the Babylonian times, the seven planets. By the time of the first century BC the Jewish seven-day week seems to have been put into place throughout Rome.