According to a tradition transmitted by the Coptic calendar still in use during the last century, the Nile's flood was announced during the 'Night of the Drop' at which time a 'tear of Isis, coming from Heaven, falls in the river, causing it to swell'. Plutarch writes that the souls of the divine entities shine in the stars: Sirius is the one consecrated to Isis, for it brings the water.' Similarly , the constellation of Orion, which appears just before the Dog Star (Sirius) is assigned to Osiris.
How to explain the extraordinary advance of Amun, in Theban records dating from around the year 2000 BC to the highest rank? Prior to this time he had been, with his counterpart Amonet, the only one of the couples of the Hermopolitan Eight. Why at this moment does Amnun (the Hidden), whose sacred animal is the ram, completely supplant the older Mentu, whose sacred animal is the bull? The answer to this question is made evident by the Precession of the Equinoxes--it was at this time that the position of the sun at the Spring Equinox moved from Taurus to Aries--except that it has never yet been generally acknowledged that the ancient Egyptians were familiar with the cycle. It is interesting, in this regard, that before the Taurean era of 4200-2100 BC, during which the cult of the bull Mentu was dominant--that is to say, during the predynastic period--the Spring Equinox was in the sign of Gemini (the Twins), and there was a dual monarcy in Egypt, each part of which had a double capital:Dep and Pe in the Kingdom of the North, and Nekhen and Nekheb in the Kingdom of the South. This theme of duality, also prominent in a number of sculpted tablets dating from that period, is further confirmed by the prototype of Hermes' staff, the caduceus with its twin serpents, several examples of which, engraved in gold leaf on the handles of flint knives, have been found, amoung other places, at El-Amrah.