The Zoroastrian text, Bundahisn (can be found at http://www.avesta.org, see Blogroll), has a Horoscope of the World* for the time the Adversary (Ahriman) pierced the earth.
“(At that time) he made the world so much invisible, at noon, that [the Sky held the darkness, below and above the Earth,] just like a dark night.…Sagittarius was the house of Servants, the thief Dragon’s Tail was disposed in it…Gemini was the house of Misfortune, the Dragon’s Head was disposed in it.” The text goes on to say, “Gochihr stood in the middle of the sky, like a dragon, its Head in Gemini and Tail in Sagittarius, as there are always six constellations betwixt its Head and Tail; its motion is backward; every ten years, its tail returns there where is its head and its head returns there where is its tail.” (Stanza 5)
The head and tail are also known as the Dark Sun and the Dark Moon. These two hostile entities oppose the Sun and the Moon. They intercept the light of the luminaries and are described in the text as the head and tail of the dragon Gochihr.
What is important to note is that the entry of the Adversary into our sphere and his gaining power over mankind (mankind fell) coincides with the beginning of celestial motion. At that time the head of Gochihr was in the mutable sign Gemini and the tail in the mutable sign Sagittarius. This event was accompanied by an eclipse.
Dear reader, you may have wondered why in older Tables of Dignities the Dragon’s Head is shown exalted in Gemini and the tail in Sagittarius. If you look at the Horoscope above, you will find that this is identical to to their position in the chart. I imagine that this was copied from one text to the next and that at some point the source was forgotten. I strongly think that this is the source. The text also helps us understand the 24th Centiloquium of Hermes Trismegistus, which says:
“Gemini and Sagittarius obey the head and tayl of the Dragon, more than other Signes: therefore do they work more mischief in those Signes, than they do in any other.”
*I’ll post an article on this at a later date.