By the late 13th century, Florence was feeling peevish: Its archrivals Siena and Pisa sported huge, flamboyant new cathedrals while it was saddled with the tiny 5th- or 6th-century Santa Reparata. So, in 1296, the city hired Arnolfo di Cambio to design a new Duomo, and he raised the facade and the first few bays before his death (probably around 1310). Work continued under the auspices of the Wool Guild and architects Giotto di Bondone (who concentrated on the bell tower) and Francesco Talenti (who expanded the planned size and finished up to the drum of the dome). The facade we see today is a neo-Gothic composite designed by Emilio de Fabris and built from 1871 to 1887.
The Duomo’s most distinctive feature is its enormous dome ★★★ (or cupola), which dominates the skyline and is a symbol of Florence itself. The raising of this dome, the largest in the world in its time, was no mean architectural feat, tackled by Filippo Brunelleschi between 1420 and 1436. You can climb up between its twin shells for one of the classic panoramas across the city—something that is not recommended for claustrophobes or anyone lacking a head for heights. At the base of the dome, just above the drum, Baccio d’Agnolo began adding a balcony in 1507. One of the eight sides was finished by 1515, when someone asked Michelangelo—whose artistic opinion was by this time taken as cardinal law—what he thought of it. The master reportedly scoffed, “It looks like a cricket cage.” Work was halted, and to this day the other seven sides remain rough brick.
The cathedral is rather Spartan inside, though check out the fake equestrian “statue” of English mercenary soldier Sir John Hawkwood painted on the north wall in 1436, by Paolo Uccello. Most of the treasures that used to be inside the building are now enshrined in the excellent Museo dell'Opera del Duomo, on the east end of the square and included in the 18€ ticket that also includes a visit to the Baptistery and the top of the dome.