Two shells, one inside the other, with the stair to the top running in the gap between them. The brickwork is laid in a herringbone bond that locks each course into the one below, so the shell could rise with no scaffolding underneath it — the problem that had left the crossing open for over a century.
463 steps, no lift, one way. It is the only place you can see how the thing is actually put together, because the herringbone is buried inside the wall.
Closed in 1436 and consecrated that March; the lantern on top was finished after Brunelleschi died in 1446, and Verrocchio's gilded ball was raised in 1471.
⭐ Its own view is the only one in Florence without the dome in it. If you want the dome in the photograph, climb Giotto's campanile instead — or as well.
Brunelleschi's Dome in pictures
