The design is not entirely unusual because there are other Roman buildings which have a similar configuration, but the size is unusual.
Inside the Pantheon The building design is one of a large round shape very much like a large barrel with a dome covering the top. Layers of beautiful thin brickwork cover the outside, round walls.
Small access holes appear occasionally in the wall which were used during construction to frame interior voids.
Now, it is exposed to acid rain and fumes from passing automobiles and overshadowed by buildings of inferior taste; but, with trust in the future, the Pantheon will survive.
Unrecognized, the design of this ancient concrete building reveals unparalleled features not encountered in modern design standards.
And from the floor to the top of the opening in the dome is the same distance.