Contradictory Descriptions of the Black Gate.

[JeffF.]

I've long wondered at the contradictory descriptions of the Black Gate between the Two Towers and Return of the King. In the Two Towers on the first page of the chapter the Black Gate is Closed it plainly says that there was a single iron gate in the stone rampart that Sauron had built across the pass but in Return of the King, The Black Gate Opens (p.200 of the Ballantine paperback) it states that there were three vast doors under frowning arches and on page 206 it again refers to 'doors' as the host ten times and more than ten times the size of Aragorn's force issues from them.

When I first noticed this WAAAY back in college my architecture major roommate pointed out the weakness in my theory that the single iron gate might have had three doors as components (one left door, one right door that opened left and right respectively and a center door between them that hinged upwards like a reverse drawbridge). He pointed out that the book states that each door was under its own arch and that the purpose of arches are to distribute weight on both legs of the arch so that a weight bearing column must be under each of the two legs of every arch and therefore they would not have been components of a single gate.

I'm hoping that someone here can provide a better explanation and description that reconciles and/or integrates the 'single iron gate' and 'three vast doors' descriptions.