Oceanus was the eldest of the twelve Titans, the great freshwater river that was conceived by the early Greeks as encircling the entire flat disk of the earth — the world-river, beyond which lay the kingdoms of the dead and the realms of myth. He was the husband of his sister Tethys, and father by her of three thousand Oceanid nymphs (the rivers and streams of the world) and three thousand Potamoi (the river-gods). Unlike his brother Cronus, Oceanus did not join the war against the Olympians; he sat out the Titanomachy in his own waters, and in consequence was not imprisoned with the rest of the defeated, but continued to flow as the encircling river of the world. In the Iliad Homer calls him "the origin of all gods," perhaps preserving a memory of an earlier cosmogonic tradition in which Oceanus, like the Mesopotamian Apsu, was the freshwater abyss from which all things proceeded. The geographical conception of Oceanus as the encircling river was eventually replaced by the more accurate notion of a great outer sea, but the name persisted; our word "ocean" descends from his.