When a dome is too heavy, the sides push outward, and cracks appear throughout the bottom portion of the structure. Engineers often wrap iron rings, called tension rings, around domes. Like hoops ...

In the summer of 1423, just before a wooden tension ring was to be laid around the dome, Brunelleschi suddenly took to his bed, complaining of severe pains in his side. When the baffled carpenters ...

Adding steel rings will help support the dome -- but it will cost a fortune! Tension rings made of steel act like hoops on a barrel and prevent the arches in a dome from thrusting outward.

Question: If the dome is to be replaced ... be done around the "critical structural issues," which includes the tension ring around the base of the elliptical dome. Everist said the plan is ...