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I'd like to argue that the dada tower and the Turris Magnus are separate towers. It's true that on the marauders map, it shows the dada classroom in this "Turris Magnus" with a shape similar to the curving room in the movies, and it's also true that when it zooms out of the triwizard tournament in movie four, it seems to show the dada classroom as in the tower now pictured on the Turris Magnus page. However, the map also shows VERY clearly, in the very upper right corner, that this circular tower called the Turris Magnus is one and the same as the grand staircases tower. It is in the right place relative to the clocktower and lookout tower (called the Turris medius, a whole nother issue), has dumbledores three towers coming out the southwest side of it, and even has a bit of the viaduct courtyard showing. Not only that, but the grand staircase tower, which I contend is the Turris Magnus, is the largest tower in Hogwarts, which the article itself even acknowledges is the usual usage of the term Turris Magnus. The map makers clearly intended the grand staircase tower to be the Turris Magnus, and since the map uses lots of Latin terms instead of the official production terms, it's perfectly plausible that though the tower is officially called the marble/grand staircase tower, it was referred to once upon a time as the Turris Magnus. I strongly suspect that the map makers didn't consult every movie to see which tower each classroom was implied to be within, and I think they just threw it in there as a way to use up space. Here's a map to show what I mean. Venus rover (talk) 02:44, July 1, 2015 (UTC)
I'd agree with the above comment. It seems evident beyond doubt that the propmakers intended the Grand Staircase Tower to be the one labelled Turris Magnus, and it is a far easier explanation that they simply misplaced the DADA classroom. -- Seth Cooperowl post! 14:07, July 1, 2015 (UTC)