In particular, the pyramids of Egypt and European cathedrals have been standing for centuries and millenia without collapsing. That can't be from dumb luck. Are they over-engineered?
Edit: algebra and calculus.
you dont actually need calculus to make sure a building wont fall down. rules of thumb developed from trial and error are sufficent.
the finer mathematical points serve more as gains in efficiency and hard proof than strict design methods.
Even today most engineering will apply a "factor of safety" and simply multiply the result by say 1.2 or 2, or sometimes 15, just in case.
As well bearing capacity of solid rock isnt really an issue at human scales.
That being said even in ancient greece (?) they did have iterative methods that approximate differentiation and integration, and trigonometry.
A good example of the trial and error nature is probably the bent pyramid, with the angle of the sides changing part way through construction