The Pantheon - The first temple to sit on the site where the Pantheon now is was built between 27-25 B.C., and commissioned by Marcus Agrippa, who was Augustus Caesar's close friend, and commander at the Battle of Actium. They built the temple to commemorate their glorious victory over Marc Antony and dedicated it to Mars and Venus. But the temple burned in the great fire of 80 A.D. (not quite as severe as the one in 64, but still bad). It was rebuilt by Domitian, but that one also burned down in 110. And so a third temple was built starting in 126; the one which still stands today. But it looked nothing like the original. And it was dedicated to all the Roman gods, not just Mars and Venus (thus the name Pantheon). This new one was so impressive, it became one of Rome's most famous buildings. It's also is one of the best preserved from the days of the empire. From the outside, the Pantheon is not especially impressive. It is the inside that makes it so special. A huge rotunda with a very high vaulted ceiling. And in the center of the ceiling, an opening called an oculus (Latin for eye). The intention is to create the sensation of standing outside even though one is inside. And the domed ceiling is meant to represent the sky, and the oculus the sun. The rotunda is a near perfect sphere measuring 142 ft (43.3 m) in diameter. It's so large that the oculus looks rather small even though it is 27 ft (8.2 m) in diameter. It serves as the only source of natural light for the interior. The ceiling weighs 5,000 tons (4,535 metric tons). It would weigh more than that were it not for the coffers carved into it. Eight barrel vaults dispersing that weight to the temple's massive walls prevents it from caving in. Looking at the building from the outside, one would never guess that it could house such a massive room. The walls have seven niches decorated with Corinthian columns, which housed statues of seven Roman gods. In the Middle Ages, the Pantheon was converted to a church and the Roman gods were replaced with statues of seven famous martyrs.