Though it was a purely mathematical system which only attempted to give a basis for computing celestial motions, Ptolemaic astronomy is of great importance historically as it remained the foundation of theoretical astronomy for more than 1400 years. Throughout the long dark centuries of the Middle Ages it survived in the studies of the retired students of the monasteries and of the few exceptionally enlightened men who still had some regard for pagan learning in the days when many of the Church Fathers denounced it as heretical. Ptolemy was the last of the great original Greek astronomers. The Alexandrian school produced, after him, only copyists and commentators, and the theoretical astronomy of the Greeks, so highly perfected in Ptolemy's _Almagest_, was for many centuries almost entirely neglected. The Roman State gave no encouragement to the study of theoretical astronomy and produced no new school of astronomy. Although it was the fashion for a Roman to have a smattering of Greek astronomy, and famous Latin authors like Cicero, Seneca, Strabo and Pliny wrote on astronomy, yet the Romans cared little for original investigations and contributed nothing new to the science. The Romans, however, appreciated the value of astronomy in measuring time, and applied to the Alexandrian school to satisfy their practical need for a calendar. What Julius Caesar obtained from the Alexandrian Sosigenes, he greatly improved and gave to the Empire, as the calendar which, with the exception of the slight change made by Gregory XIII, we still use. The pseudo-astronomical science of astrology, or the so-called 'judicial astronomy' was pursued during the Roman Empire and throughout the Middle Ages with much greater zeal than theoretical astronomy. The interest in astrology, to be sure, encouraged the study of observational astronomy to a certain extent; for the casting of horoscopes to foretell destinies required that the heavenly bodies be observed and methods of calculating their positions at any time or place be known. But there was no desire to inquire into the underlying laws of the celestial motions or to investigate the real nature of the heavenly phenomena.