The duomo took 600 years to be mostly complete and still has work being done though mostly restoration and maintenance. It has a marble quarry dedicated solely to it. Absolutely magnificent building, I did all the tours a few months ago, loved it.

That is why we don’t build buildings like it anymore, insanely expensive and time consuming. Plus our current rich people would rather rape kids on their massive yachts and private island than commission beauty to be admired by wider society like the wealthy of old.