>>11707482Often engineers of the past wold create elaborate, calculated models of the things they were going to construct with the weight of parts of the real structure being in a proportion to the model. They also had all sorts of smart tricks developed over many years to help them determine if things like arches are going to stand.
As for why old buildings still stand is because they were made well. Poorly built buildings would collapse and unlucky good buildings could burn down or be destroyed in another way. The UK is great for old buildings. Some random cottages in the country side or random bars are sometimes up to 700 years old.
St Peters Chapel in England was built in 654 AD.
