This is worth a watch: http://www.youtube.com/watch?v=lXt2-xi2yLc

I saw the whole programme over Christmas, he was saying that one of the problems with stone is that the higher you went, the larger the base had to be to stop the whole thing toppling over. Hence the design of the pyramids and the flying buttresses (which are base extensions) to ensure that the whole structure was kept under compression (stone is no good under tension).

I love those massive fantasy buildings. I guess we all have our 'credulity breaking point' and on this subject mine is beyond Pluto. Give me cities with populations of millions and just one field, give me 600 foot high statutes! Give me vast populations living in underground caverns with no natural light! (Tolkien's dwarves must have all had rickets)! I love it all!!