 At the summit is an ocular opening across which provides light to the interior.Bramante's plan for the dome of St. Peter's (1506) follows that of the Pantheon very closely, and like that of the Pantheon, was designed to be constructed in Tufa Concrete for which he had rediscovered a formula.With the exception of the lantern that surmounts it, the profile is very similar, except that in this case the supporting wall becomes a drum raised high above ground level on four massive piers.