Duomo dome
Impressive, although a number of large cracks were evident. Because of its size, the dome couldn't be constructed as 'normal' using timber scaffolding. The architect studied the Pantheon in Rome which also had a large dome, to get engineering inspiration. In the end Brunelleschi convinced the city fathers that he knew what he was doing but he ensured his longevity on the 18-year build by keeping most of the plans in his head.