The Santa Maria del Fiore (meaning Saint Mary of the Flowers), also known as the Florence Cathedral, is the main church in the city of Florence in Italy. It is the third largest church in the world (and also in Europe) and was designed by Arnolfo di Cambia in what was a daring attempt to build one of the largest cathedrals known to Christianity.
The new cathedral was built over the old church of Santa Reparata and it took a good 140 years to be completed (started in 1296, finished in 1436). There were a few reasons for the prolonged construction. For one, in the 1350s the Black Death killed most of the population that would otherwise have been taking part in the construction of the cathedral. It was only during the 1360s to 1380s, therefore, that the building was really up and running.
No, perhaps the biggest challenge was still the dome of the cathedral. A big building such as the Santa Maria del Fiore would require an even larger roof (or dome), but during the 1400s people did not know how such a humongous structure could be made. By 1418, he church remained uncompleted simply because of the dome nobody knew how to build. It was such a baffling task that "even the original planners of the dome had been unable to advise how their project might be completed” (King, "A More Beautiful and Honourable Temple", pg.5)
After decades of procrastination, there was only one solution left to them, it seemed. In 1418 the Opera di Santa Maria del Fiore announced a competition to successfully erect a dome for the problematic cathedral. Whoever whose idea was used would earn a reward of a whopping 200 gold florins (one florin is around USD$140 in today's currency). Naturally, the competition attracted a lot of attention. Architects from all over headed to Florence to submit their ideas.
Enter the most unlikely candidate ever - a forty-one-year-old goldsmith and clockmaker named Filippo Brunelleschi. Never mind the one dome that had already troubled almost everyone in Florence, Brunelleschi announced that he could build two domes (quoted from the Museum Florence):
Brunelleschi's astonishingly innovative approach involved vaulting the dome space without any scaffolding by using a double shell with a space in between. The inner shell (with a thickness of more than two metres) is made of light bricks set in a herringbone pattern and is the self-supporting structural element while the outer dome simply serves as a heavier, wind-resistant covering.
...but refused to elaborate on how this could be achieved, for fear of his ideas being stolen. Finally, in 1420 (after shouting down his opponents), Brunelleschi, who was already known as a genius, won the competition and work on the dome finally got started. Simply put, Brunelleschi was "the first person to think about constructing rational space" (Joost-Gaugier, "Introduction", p.6). It took sixteen years to finish the dome alone, but finally, on 25th March 1436, the cathedral was consecrated by Pope Eugene IV.
It took nearly 140 years for the completion of the cathedral but it seemed worth it. It was certainly the largest church in Europe at the time, as it had set out to be. It had definitely been an impressive feat for architects of the time, and the result was certainly "a more beautiful and honourable temple than any other existing in Tuscany" (quoted in Brown, "Italian Communes and City-States, c. 1300", pp.17)