The Towers of Midnight are the Forsaken. In chapter 3, Egwene has a dream about 13 towers, falling one after another, leaving only six remaining, each of which grow more powerful as the others fall. Including one almost falling, then rising up higher than any of the others(moridin). It is the forsaken. Well, maybe the Tower of Ghenji too, and possibly even the black tower, though there isn't a whole lot on the black tower in the book. Most WoT titles refer to multiple things, both literal and metaphorical.