Under-way

The Tower of Cirith Ungol was raised by the early Gondorians as part of their guard on Mordor at the end of the Second Age. We do not know whether it was these original builders who also created the Under-way that connected the Tower to Shelob's Lair. On balance, it seems rather more likely that the tunnel was installed by the Orcs after the Tower fell into the hands of the Enemy, some two millennia after the Tower was originally raised.

The nature of this slab is not explained in any detail (because it is described from the perspective of Sam Gamgee, who had little opportunity to inspect its workings). It is clear, however, that the slab was connected to some kind of mechanism that allowed the Orcs to move it aside and so pass through before closing the tunnel again. (Sam heard a rumbling noise and then a bump, which must have been caused by the slab moving into position.) The slab - or stone door - could also apparently be locked closed with some kind of latching mechanism, and even when closed, it did not fill the entire height of the tunnel. At the top of the slab was an open space, small enough that there was no danger of Shelob passing through, but large enough to be used by an Orc (or a Hobbit) who urgently needed to pass the closed slab from the outside.