Brunelleschi's astonishingly innovative approach involved vaulting the dome space without any scaffolding by using a double shell with a space in between. The inner shell (with a thickness of more than two metres) is made of light bricks set in a herringbone pattern and is the self-supporting structural element while the outer dome simply serves as a heavier, wind-resistant covering. The dome is crowned by a lantern with a conical roof, designed by Brunelleschi but only built after his death in 1446, while the gilt copper sphere and cross on top of the lantern, containing holy relics, was designed by Andrea del Verrocchio and installed in 1466.
The inner shell of the dome was frescoed by Giorgio Vasari and Federico Zuccari from 1572 to 1579, the subject matter chosen, namely the Last Judgement, reflecting the iconography adopted in the baptistry. The frescoes on the inner shell of the dome were the object of a thorough restoration between 1978 and 1994.