The Eye: what was it?

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Thanks for the comments, I'll try to respond to some of them later on. For now I'd like to throw this passage into the mix. It is from the description of Minas Morgul, and seems somehow relevant:

Originally Posted by LotR; The Stairs Of Cirith Ungol

...the topmost course of the tower revolved slowly, first one way then another, a huge ghostly head leering into the night.

A revolving, peering turret is perhaps a common feature in Dark Towers?