St. Peter's Basilica
When Pope Julius decided to build the "grandest church in Christendom" the design by Donato Bramante was chosen, and Pope Julius laid the foundation stone in 1506. Bramante's plan was in the shape of an enormous Greek Cross, which means that it had four arms all of equal length, and a large dome at the middle. For the next hundred years, the groundplan got changed backwards and forwards between a "Greek Cross" like Bramante's plan and a "Latin Cross" like the old basilica, but one thing never changed, and that was the idea of having an enormous dome at the place where the two arms crossed.