http://gnosis.org/library/marcion/Tert5.html#AM202Now of what God did the Legion testify that Jesus was the Son? No doubt, of that God whose torments and abyss they knew and dreaded. It seems impossible for them to have remained up to this time in ignorance of what the power of the recent and unknown god was working in the world, because it is very unlikely that the Creator was ignorant thereof. For if He had been at any time ignorant that there was another god above Himself, He had by this time at all events discovered that there was one at work below His heaven. Now, what their Lord had discovered had by this time become notorious to His entire family within the same world and the same circuit of heaven, in which the strange deity dwelt and acted. As therefore both the Creator and His creatures must have had knowledge of him, if he had been in existence, so, inasmuch as he had no existence, the demons really knew none other than the Christ of their own God. They do not ask of the strange god, what they recollected they must beg of the Creator--not to be plunged into the Creator's abyss. They at last had their request granted. On what ground? Because they had lied? Because they had proclaimed Him to be the Son of a ruthless God? And what sort of god will that be who helped the lying, and upheld his detractors? However, no need of this thought, for, inasmuch as they had not lied, inasmuch as they had acknowledged that the God of the abyss was also their God, so did He actually Himself affirm that He was the same whom these demons acknowledged--Jesus, the Judge and Son of the avenging God.
It is the same identical argument used by modern skeptical critics against the Christian apologists: if Jesus was really how the Gospel Jesus is described, why wasn't he noted by Josephus etc ?
And surely, for Tertullian, the Creator God had a better eye than Josephus etc.
En passant, it is curious the use of the expression ''God of the Abyss'' referred to the Creator. Is it a coincidence that the demons fall on the lake that is symbol of the Abyss?
The irony seems that the demons are doomed to go where they did fear more of all (and that was the sense of their request to enter into the swine): into the Abyss of their god, the Creator.