He designed two domes—a thick inner shell to support the weight and a lighter outer shell to protect it from the elements.
By the early 15th century, the Santa Maria del Fiore cathedral was a source of civic embarrassment. It had sat roofless for decades because no one knew how to build a dome large enough to cover its 143-foot-wide opening without the walls collapsing. Traditional Gothic flying buttresses were forbidden in Florence—they were seen as "German" and ugly. The city needed a miracle. The Medici Gamble
When the dome was completed in 1436, it was the largest in the world. For the Medici, it was a triumph. The dome became a physical symbol of the "Medici Golden Age," visible from miles away, signaling that Florence—and the family that funded it—was the center of the civilized world.