[saalweachter]

Well, there's also good old "trial and error".

A lot of impressive feats from way back when were accomplished more by experienced extrapolation than by deep understanding. In the case of those churches, they built a lot of churches, with a lot of different designs. Each new architect would try to build something a little bit taller, a little bit thinner and more ambitious than his predecessors, without really understanding the mechanics of the structures. Sometimes they pushed too far, and buildings collapsed and people died. Sometimes they were too cautious -- I've heard the Brooklyn Bridge is hilariously over-engineered, because of the lack of computer modeling. What we see today are the best of the best, the most ambitious ones that didn't fall down. The ones that were too unambitious or which were too ambitious to succeed have been forgotten.