This paper looks at the concurrent spread of astrology and the seven-day planetary week in the Graeco-Roman Mediterranean from the last century BCE through Late Antiquity. During this period astrology became increasingly pervasive in all aspects of life and among members of all levels of society. Astrology was not only a system of divination claiming to predict the future by observing the stars: it implied a religious conception of the world, its starting point being the faith in celestial divinities that were thought to exert an influence on the world. The Sun, the Moon, the planets, and other astral phenomena were understood as divine powers affecting the life and fate of human beings. In the planetary week, each day was named after one of the seven non-fixed heavenly bodies of the universe, as it was known in antiquity: Saturn (Saturday), Sun (Sunday), Moon (Monday), Mars (Tuesday), Mercury (Wednesday), Jupiter (Thursday), and Venus (Friday). In turn, the five planets and the two luminaries (the Sun and the Moon) had been named after Greco-Roman gods and goddesses and were themselves regarded as celestial deities, following the near eastern tradition that identified the heavenly bodies with specific divinities. This chapter argues that the growing familiarity, from early imperial times onwards, with astrological concepts and practices along with the use of the seven-day planetary week as a means for measuring time, contributed to the diffusion of astral beliefs and the cult of the seven planets as week deities in the Graeco-Roman world during the imperial and late antique periods.
