5:29 It was an architectural design to build the Pantheon of progressively lighter materials to reduce the load on the supporting walls. Not to save time and money!
Interesting! When I was living in Rome I very often when to have my coffee in the square as I always enjoyed watching the pantheon with fascination! Easley one of my favorite construction so full of history!
I was there last week, and the ceiling of the dome looks much cleaner (downright new looking). It looks entirely like that one bit you can see at 6:25.
@ 6:16 - The dome roof was built up in stages (or imagine rings) with the largest ring made with the heaviest material then each ring becoming lighter in stages before reaching the domes Oculus.
if you ask to Roman citzens where the ''Pain-thee-on'' is located, they probably do not understand you (pronounce mispelled): in Rome it sounds: ''P-AAA-nTe-on''.
Unfortunately they took all the wonderful decorations off it and striped this monument naked. By the way. His shoes are terribly ugly, no one is allowed to wear those ugly shoes in Rome!