The most beautiful Cathedral in Christendom?

Florence's Duomo always takes my breath away each time I see it. While it may not be the most beautiful cathedral in all of Christendom, its pink, green and white marble exterior never fails to impress.

Begun in 1296, it took close to 150 years to complete. The dome a architectural marvel of its time was the work of Filippo Brunelleschi. It was constructed between 1420 and 1436 and to the best of my memory has withstood the test of time for almost 600 years (Don't know what bombing in World War II did to it)