Was the Pantheon oculus covered?

Dr. dig responds:
There was no glass in the oculus of the Pantheon, and rain just came through the opening. The floor was marble, and slanted to allow for drainage through pipes. In fact, remarkably little rain enters through the oculus -- perhaps because the rain rarely ever falls straight down, but is always blown at an angle and therefore doesn't manage to enter the open space at the top as it might do entering an open window on the side of a house.