One also wonders if the tunnels where the circles of Minas Tirith passed through the 'keel' were barred by gates and/or potcullises, and whether galleries with loopholes and murder-holes were installed.
I know I would have
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Whatever stone was used for the outer wall, and Orthanc, it wouldn't have been marble, which is a rather soft stone, and which vegetation can tear up pretty easily (as can be seen in any old graveyard). For Orthanc basalt is a a candidate, being hard, dense, black and capable of a high polish; the uneroded basalt "necks" of old volcanoes provide the crags on which many fortified places in southern France were built. But a comparable white stone?
Of course, one can't push Middle-earth MagiTech(tm) too hard. Seriously- try to find a metal as ductile as copper but simultaneously harder (and lighter) than steel........