Anu was the visible sky, but he also represented the invisible heaven, which was supposed to extend above the visible one, and to be the abode of the gods. The chief seat of his worship was Erech, where he was regarded as the oldest of the gods, and the original creator of the universe. But elsewhere, also, he was looked upon as the creator of the visible world, and the father of the gods. By his side, in the Semitic period, stood the goddess Anat, whose attributes were derived from his. The worship of Anat spread from Babylonia to the Canaanites, as is shown by the geographical names Beth Anath, 'the temple of Anat' (Josh. xix. 38; xv. 59), and Anathoth, the city of 'the goddesses Anat.' It was even introduced into Egypt after the Asiatic wars of the eighteenth dynasty. In the præ-Semitic days of Chaldea, a monotheistic school had flourished, which resolved the various deities of the Accadian belief into manifestations of the one supreme god, Anu; and old hymns exist in which reference is made to 'the one god.' But this school never seems to have numbered many adherents, and it eventually died out. Its existence, however, reminds us of the fact that Abraham was born in 'Ur of the Chaldees.' Ea originally represented the ocean-stream or 'great deep,' which was supposed to surround the earth like a serpent, and by which all rivers and springs were fed. He was symbolised by the snake, and was held to be the creator and benefactor of mankind. One of his most frequent titles is 'lord of wisdom,' and the chief seat of his worship was at Eridu, 'the holy city,' near which was the sacred grove or 'garden,' the centre of the world, where the tree of life and knowledge had its roots. It was Ea who had given to mankind not only life, but all the arts and appliances of culture also, and it was his help that the Babylonian invoked when in trouble. He was emphatically the god of healing, who had revealed medicines to mankind. As god of the great deep, he was often figured as a man with the tail of a fish, and in this form was known to the Greeks under the name of Oannes or 'Ea the fish.' Sometimes the skin of a fish was suspended behind his back. Oannes, it was said, had in early days ascended out of the Persian Gulf, and taught the first inhabitants of Babylonia letters, science, and art, besides writing a history of the origin of mankind and their different ways of life. His wife was Dav-kina, 'the lady of the earth,' who presided over the lower world.