One of Rome's most impressive and best-preserved ancient monuments, the Pantheon is particularly close to the hearts of Romans. The emperor Hadrian designed it around AD 120 and had it built on the site of an earlier temple that had been damaged by fire. The most striking thing about the Pantheon is not its size, immense though it is (until 1960 the dome was the largest ever built); rather, it is the remarkable harmony of the building. Notice that the height of the dome is equal to the diameter of the circular interior. The oculus, or opening in the ceiling, is meant to symbolize the all-seeing eye of heaven; in practice, it illuminates the building and lightens the heavy stone ceiling. The original bronze doors have survived more than 1,800 years, centuries longer than the interior's rich gold ornamentation, which was plundered by popes and emperors. Art lovers can pay homage to the tomb of Raphael, who is buried in an ancient sarcophagus under the alter of Madonna del Sasso. COST: Free.