When Alexander approached the city, however, he was met by a deputation of Chaldean astrologers. The astrologers were a class of philosophers who pretended, in those days, to foretell human events by means of the motions of the stars. The motions of the stars were studied very closely in early times, and in those Eastern countries, by the shepherds, who had often to remain in the open air, through the summer nights, to watch their flocks. These shepherds observed that nearly all the stars were _fixed_ in relation to each other, that is, although they rose successively in the east, and, passing over, set in the west, they did not change in relation to each other. There were, however, a few that wandered about among the rest in an irregular and unaccountable manner. They called these stars the wanderers--that is, in their language, _the planets_--and they watched their mysterious movements with great interest and awe. They naturally imagined that these changes had some connection with human affairs, and they endeavored to prognosticate from them the events, whether prosperous or adverse, which were to befall mankind. Whenever a comet or an eclipse appeared, they thought it portended some terrible calamity. The study of the motions and appearances of the stars, with a view to foretell the course of human affairs, was the science of astrology.