@SCP_Hughes I don't find the surprise! 10 foot shorter theory, or the real columns ending up in the bottom of the mediterranean and these being substitutes, to pass muster (especially when you consider the masonry coursing). There are other possible reasons for its appearance, though. fwiw
@SCP_Hughes My own reading of the Pantheon in terms of formal design is the fusion of the building typologies on the processional route from mausoleum to pantheon, The key is to read the intermediary block between the rotunda and the portico as a giant triumphal arch with quadriga.
@SCP_Hughes Think analogically. Take the forecourt portico and the midcourt triumphal arch and re-present them processionally together attached to the rotunda. And consider that the quadriga would have been largely obscured by a taller portico from the approaching perspective.
1/ Architecture is not "building" per se. It is the analogical re-presentation of the space of our world and how we perceive and inhabit that space and orient ourselves in-and-beyond it. The objectification of space as patterned and oriented. (Lonergan, Eliade).
2/ The ancient painted caves can be understood as naves of underground cathedrals (sanctuaries), whose ceilings are analogous to frescoed vaults. It re-presents the space of their world and their place within as cosmologically understood. As above, so here, so below. Analogical.