The Pantheon is Rome's most well preserved Roman monument. It was considered by the Romans to be their greatest architectural achievements and to this day boasts the world's largest unreinforced dome. Although the exterior with its 16 stone Corinthian columns is the sight you will be most familiar with, stepping through the bronze doors and looking up to the dome is equally as impressive. It was built over 2000 years ago as a temple to all of the Gods of Ancient Rome, but now functions as a church. The bronze tiles that used to cover the dome are can now be found at St Peter's Basilica.