Duomo
It started life in 1294 when the city's ruling religious elite felt they needed to keep pace with newly commissioned cathedrals in Sienna and Pisa. The architect Arnolfo di Cambio was given a simple brief to create the largest church in the Roman Catholic world and "surpass anything of its kind produced by the Greeks and Romans in times of their greatest powers." No pressure then!
Little wonder it was 123 years, and a few generations of architects, later that construction reached a stage where work on the dome could begin. The one minor oversight was that building had plowed ahead for more than a century without anybody figuring out how the dome could be constructed. Nobody seemed deterred when di Cambio's original scale model collapsed under its own weight. Proposed solutions included filling the cathedral with earth mixed with coins, building the dome around the mound and then inviting the population to later carry away the dirt (with the incentive of finding a few coins).
Eventually it was a goldsmith and clockmaker, Filippo Brunelleschi, who solved the dilemma with some new architectural, construction and tiling techniques. It is still the world's largest masonry dome.
There is nothing inside the Duomo to match the exterior masterpiece but you can climb between the dome's "twin shells" to a viewing platform that overlooks the city.
At ground level, the smaller and older Baptistry opposite the cathedral's entrance is famous for its Byzantine mosaics and golden doors depicting scenes from the old testament. The door panels are replicas—the original goldsmith masterpieces, dubbed the "Gates of Paradise," are in the Museo dell'Opera at the other end of the piazza.
