The dome is like an inverted bowl. Accurate mathematical calculation must be carried out before construction, and the stress of the whole structure must reach "perfect balance", otherwise the heavy dome will cause the circular wall supporting it to crack, and it will be over.

The concrete method is to make a hemispherical supporting structure with lighter wood first, and then build bricks from the bottom. After the brick structure is stable, the wooden shelf can be removed; Then decorate the inside and outside in turn. Buildings with domes are not ordinary, and the architects entrusted to build domes are all masters, but the dome structure is very challenging and cannot guarantee eternal success.

Take St Paul's Cathedral in London as an example. At that time, there was no architecture major in Britain, so the chief architect/designer finally elected by Congress was a man named Christopher? Ryan Christopher Wren, mathematician. Ryan collapsed twice while building a brick structure with a dome. Both times looked stable, but as soon as the wooden frame was dismantled, the brick fell like a bullet. It was not until the third time that the structure stabilized.

The dome of St. Paul's Cathedral is so huge that it can't be supported by foundation or circular wall if classical construction methods are adopted. Ryan then adopted "cable dome structure" and hollow composite dome structure. St Paul's Cathedral is really a classic building with both internal and external repair!