Question

Why was the pantheon constructed with a 30-foot-diameter oculus (hole) in its roof?

Answer 1

The rotunda’s internal geometry would create a perfect sphere since the height of the rotunda to the top of its dome would match its diameter: 142 feet (43 m). At its top, the dome would have an oculus or eye, a circular opening, with a diameter of 30 feet (9.1 m), as its only light source.