The sun and the moon were worshipped everywhere; each city had its own sun-god and its own moon-god. The preference generally shown by nomads for the moon, since their journeys are made by night, is kept up in early Babylonia, where the moon-god is regarded as the father of the sun-god, and as the greater being. In Ur of the Chaldees the moon was the principal deity. There were also towns such as Larsa and Sippara, where the sun was the chief god; and many of the great gods of later times were originally sun-gods. The Chaldeans, moreover, were proverbially star-watchers, and a "zigurrath" or observatory, a building of seven spheres corresponding to those of the planets as they pass through the signs of the zodiac, and like them rising up to the seat of God at the North Star, was a regular part of the later Babylonian temple. To Babylonia is due the practice of the orientation of temples; that is to say, the arrangement of the building in such a way that its principal axis shall point exactly in a desired direction. Some of the Babylonian temples were oriented so that the sun should shine to the western end of them on the day of the spring equinox when the inundation of the rivers began on which the prosperity of the country so much depended. The temple was thus an astronomical instrument of a high degree of accuracy, and the priests who directed its building and served in it when built were men of science and learning. A religion which is connected with the heavenly bodies, though it does not fully supply the needs of the lower orders and has too little energy to cope with superstition, tends to produce a priesthood who form centres of enlightenment and civilisation throughout the country. This was in the highest degree the case in Babylonia. To these old astronomers the world owes the signs of the zodiac, which were fixed not later than in the fifth millennium B.C., and in which we see how early man beheld in the nightly heavens the creatures which on earth he regarded as divine, so that he worshipped them in both regions. The institution of the Sabbath is also Babylonian; whether it was connected with the changes of the moon, or with a week of days named after the seven planets, is not certain. Seven is a sacred number in Babylonia, as we find in many a connection.