The most fascinating part of the Pantheon is its giant dome, with its famous hole in the top (The eye of the Pantheon, or oculus). The dome was the largest in the world for 1300 years and to present remains the largest unsupported dome in the world. Its diameter is 43.30 meters.
The interior of the dome was possibly intended to symbolize the arched vault of the heavens. The oculus at the dome’s apex and the entry door are the only natural sources of light in the interior. Throughout the day, light from the oculus moves around this space in a reverse sundial effect: marking time with light rather than shadow. The oculus also offers cooling and ventilation; during storms, a drainage system below the floor handles rain falling through the oculus.
