Despite Florence's urban sprawl and the fact that it's a city surrounded by modern neighborhoods, the Cathedral's dome has dominated the city for almost six centuries, and you can see it from far away.
Its designer Brunelleschi was the competition winner of 1418, and his designs obviously started out from the beautiful structure that had been set over a century earlier by Arnolfo di Cambio: the huge octagon surrounded by three symmetrical domes, which are also on an octagonal base and covered with red tiles.
To avoid complicated and dangerous scaffolding, Brunelleschi offered a revolutionary solution: he set a dome with a double shell, one on the outside for protection from the weather, and an internal one connected to the external dome by white ribs that vividly contrast the dark red bricks.
The structure was finished in just over fifteen years and solemnly consecrated in the presence of the Pope. At that time the Cathedral was named Santa Maria del Fiore, in homage to the Latin name of the city that in fact comes from the word "fiore", or flower. The dome is 107 meters tall. The small temple with columns that you see on top is called the "lantern" and was added in the following decades, just like the large gilded copper sphere that was hoisted thanks to advice from the great Verrocchio.
As demonstrated by the objects kept in the Museo dell'Opera del Duomo, or Cathedral Works' Museum, Brunelleschi personally supervised every technical detail of the dome's construction, from the diameter of the cables, to the pulley system, up to the shape of the molds for the bricks to be placed near the steps of the staircase between the two "shells". This narrow staircase with 463 steps ascends through the crawl space between the outer and inner shells, and you can still go up them even today. When inside, go down the left side of the Cathedral where you'll first reach a balcony that offers a viewpoint of the Cathedral's entire Gothic interior. Then continue to go up between the two "shells" until you reach the roof terrace outside, 91 meters high.
FUN FACT: if you look carefully, you'll notice that just below the edge of the dome itself is an area that's partly decorated with a balustrade, and partially left bare. The interruption of the barrier built at the beginning of the 1500s was caused by Michelangelo's negative comments: when he saw the part that had been finished, he said it was like a "cage of crickets" in comparison with the majestic work of Brunelleschi.
