Raining Inside the Pantheon's Oculus

The oculus of the Pantheon is 24 feet in diameter and surprisingly is the only source of light (it is fairly bright under the dome). It represents the link between the temple and the gods above. The oculus is open to the rain, but the floor is slanted toward central drains cut into the marble floor.

One of the drains in the marble floor of the Pantheon

Here's another article that might be of interest:
The Pantheon And Campo Di Fiori
Live Cams in Italy: Seeing is Believing