No, Kanakaberaka has it right. It's the two faces of the moon. The supersized figures in the foreground who stand on this frontier are Merlin and the Pendragon as they appeared robed at the top of the staircase at St. Anne's. There is also the duality of the Merlin/Pendragon relationship here in relation to their roles "within" and "without" Thulcandra's frontier, respectively. If you will recall Denniston's discussion of the wild
otherness of certain older inhabitants of our world, who were dissabearing as the order of things polarized into specific and particular Good and Evil--- it was on the grey and rainy day they went to look up Merlin. The implication, that Merlin belongs to this older order of things, is quite plain. And somehow this order is
within the Siege, though not aligned with the Dark Eldili exactly. The wizard wore blue, per the lower, earth-and-water orbits, while the red of the Pendragon's robe is air-and-fire.
That Alcasan's-Head cover art looks almost (Same artist or design team, maybe?) like those of my
Christ Clone Trilogy books!
False ideas may be refuted indeed by argument, but by true ideas alone are they expelled. — Apologia Pro Vita Sua: Cardinal Newman
Freedom lost and then regained bites with deeper fangs than freedom never in danger. — Cicero
You don't have to burn books to destroy a culture. Just get people to stop reading them. — Ray Bradbury