This is it. This is the one piece of architecture that is universally considered to be the crowning achievement of everything the Renaissance has to offer. All other buildings were just practice running up to Saint Peter's Basilica. To this day, it is the largest church on Earth, and makes that point known by outlining the silhouettes of the world's other great churches on its floor in brass. They all fall inside Saint Peter's walls. Originally, the basilica was much smaller. But then it was discovered that the building was going to collapse. A reconstruction effort was begun in 1452, but was halted because of a lack of money. Then in 1506 Pope Julius II decided to raze the old buildings and put up the greatest church ever. A church that would be the mother church for all of Christianity. His dream was realized 120 years later when Saint Peter's was dedicated. By then the construction project had outlived all of its original architects and builders. Changes in leadership led to changes in design. By the time the project fell into Michaelangelo's hands it was well on its way to being constructed as a huge Latin cross. Michaelangelo changed direction, bringing Saint Peter's back to its original design -- a Greek cross. After Michaelangelo's death, the project passed to Giacomo della Porta, who changed direction again and is responsible for the Latin cross we see today. He is also blamed for the building's huge façade which blocks views of the magnificent dome from outside. There's just too much to say about Saint Peter's to fit it all in this capsule. Hundreds of books have been written about the church. If you do go, be sure to look for the bronze statue of Saint Peter. Catholics have been kissing his big toe for centuries.