Pantheon
(Temple of "All the Gods")

Built: 27bc to 25bc by Marcus Agrippa.

The Pantheon is the best preserved building in all of Rome. That's because it is one of the few that has been spared by religious turmoil. It was erected as a temple to honor the Roman gods. Inside, there used to be statues of all the gods ringing a ceremonial altar. That is where animals were sacrificed and burned. The smoke went out through at 27-foot-wide hole in the dome. That hole became known as the "all-seeing eye of Heaven" after early Christians took over the building around 600. They claimed to be possessed by demons whenever they walked by. Turning it into a church sanctified the land, and presumably drove the demons elsewhere. More importantly, it kept the building in favor with the rulers of the time, and spared it the indignity that befell the other great buildings of the city. Architecturally, the building is a marvel. In the second century Emperor Hadrian personally designed the building you see today to replace the earlier temple, which had burned. Construction was finished in 125, and the 20-ton bronze doors have been in service almost since then. For 1,800 years they have stood as silent sentinels greeting visitors from every land. The dome's diameter is equal to the height of the walls -- 142 feet. To support such a massive structure, the walls had to be made 25-feet thick. It was this building that Michaelangelo studied before taking on Saint Peter's, which has a dome just two-feet smaller. In fact, until 1960 it was the largest dome ever built. Any record that stands for 1,835 years has to be respected.