Astrology is the study of the positions and aspects of celestial bodies in the belief that they have an influence on the course of natural earthly occurrences and human affairs. The Chaldaeans and the Assyrians were the first to discard their sky gods in favour of a system of divination founded upon astronomy and numerology, regarding the heavenly bodies as exerting an influence upon the lives of people. Due to this, it was believed that future influences could be predicted. Astrology spread throughout the ancient Middle East, Asia, and Europe, but with the rise of Christianity, interest in astrology subsided, although astrologers continued to flourish. During the Renaissance, Astrology as a form of divination regained popularity, due in part to the rekindled interest in science and astronomy. Astrologers were held in high esteem for many years. However, in the 16th and 17th centuries, Christian theologists waged war against astrology. In 1585 astrology was officially condemned in a bull of Pope Sixtus V, and in 1631, Pope Urban VIII reinforced this with another bull. At the same time the astronomical work of such men as Copernicus, Kepler, and Galileo was undermining the tenets of astrology. Astrology, however, continued to be practiced. All of the aforementioned scientists remained practicing astrologers, as did other great thinkers such as Descartes and Newton.