The unique Octagon lantern over the crossing took 14 years to build, weighs 200 tons, and exerts a perfect perpendicular downward thrust. By 1340, its roof was covered in lead and its ceiling was carved and painted. The ceiling seen today, as well as the wooden panels painted with angels in the octagon, are Victorian renovations. These wooden panels swing open like doors (accessible on a guided tour), from which there is a vertigo-inducing view down to the floor below.
The Pantheon's huge dome is a perfect hemisphere of cast concrete, resting on a solid ring wall. Coffers cut in the inside add visual interest, but more importantly, reduce the load of the dome. The exterior is covered in almost weightless cantilevered brick. With a span of 43.2 m (142 feet), this was the largest dome in the world until the dome of Florence Cathedral was completed in 1436.
The great central dome of St. Peter's Basilica was designed by Michelangelo. It is made of brick and is 42.3 m in interior diameter (making it almost as large as the Pantheon's roof), rising to 120 m above the floor. The four piers of the crossing that support the dome are each 60 feet (18 m) across.