12. The interest attaching to this temple, wonderful as it is in itself, is greatly enhanced by the circumstance that its ruins have through many centuries been considered as those of the identical Tower of Babel of the Bible. Jewish literary men who travelled over the country in the Middle Ages started this idea, which quickly spread to the West. It is conjectured that it was suggested by the vitrified fragments of the outer coating of the sixth, blue, stage, (that of Mercury or Nebo), the condition of which was attributed to lightning having struck the building. [Illustration: 71.--BIRS-NIMRUD. (ANCIENT BORSIP.) (Perrot and Chipiez.)] 13. That the Ziggurats of Chaldea should have been used not only as pedestals to uphold shrines, but as observatories by the priestly astronomers and astrologers, was quite in accordance with the strong mixture of star-worship grafted on the older religion, and with the power ascribed to the heavenly bodies over the acts and destinies of men. These constructions, therefore, were fitted for astronomical uses by being very carefully placed with their corners pointing exactly to the four cardinal points--North, South, East and West. Only two exceptions have been found to this rule, one in Babylon, and the Assyrian Ziggurat at Kalah, (Nimrud) explored by Layard, of which the sides, not the corners, face the cardinal points. For the Assyrians, who carried their entire culture and religion northward from their ancient home, also retained this consecrated form of architecture, with the difference that with them the Ziggurats were not temple and observatory in one, but only observatories attached to the temples, which were built on more independent principles and a larger scale, often covering as much ground as a palace.