The pantheon was built as a pagan temple by Emperor Hadrian between 118 and 125 A.D. over the ruins of another temple. It was later in 609 converted into a Christian Church by Pope Boniface IV . The most recent renovation was the addition tombs of Vittorio Emanuele II, as well as Renaissance Artist Raphael.
When walking up to this giant the first most notable feature is the massive pillars and huge doors. It is only when you walk in that you realize that its focal point is its unsupported dome. I read that it is a modern marvel as to how they were able to make it with no support. I remember being humbled. This day and age we think we are just the smartest people around but if you were to take away most peoples technology and in this case, calculators. There is no chance we would be able to build something that magnificent.