Although the church was designed by Arnolfo di Cambio in 1296, the dome was not started until the 15th Century. With Cambio long dead, none of the architects at that time had any idea how to construct such an enormous structure, since the use of buttresses was forbidden in Florence and mortar took several days to set.
But all was not lost. In an amazing comeback story, Filippo Brunelleschi, an architect who had been defeated in an earlier bid to design the Baptistery doors, won the competition to build the dome. He beat out Lorenzo Ghiberti, the same artist he had lost to before.
Brunelleschi invented machines to hoist the bricks needed for the dome up to the workers and was able to construct the entire dome without using centring (a support structure to hold the dome in place while the brick were laid). Containing over 4 million bricks, the dome was completed in 1436.
The lantern was added after Brunelleschi’s death in 1446, and supposedly contains holy relics. However, there were several rumors, that, in fact, an entire tomb of unknown origin is located inside.