“The celebrated description of human proportions by Vitruvius, used to illustrate his discussion of symmetrical temple design, is directly relevant here. He describes the circle and square ideally defined by the outstretched limbs of the body, a relationship of shapes very similar to the architectural solution he prescribes for vaulted circular building….
In the the new Roman architecture, man was shown his path and place by vaults overhead as much as by plans and openings.”
William McDonald, The Architecture of the Roman Empire, Volume I.
Notably, in this book, McDonald uses an illustration of Leonardo’s Vitruvian Man, which uses a circle and a square, rather than Vitruvius’ original sketch.