Not only was it as good a solution to the idea of “just a dome over a drum” as can possibly be created Architecturally, it was also the first true concrete structure.
Aestheically, its’ précis is even more poetic in the economical use of ideas:
Seen from its north-facing front, the concrete-and-brick Pantheon consists of a pedimented entrance porch, a domed rotunda and a boxlike intermediate structure joining them. Their forms—triangle, hemisphere and rectangle—announce the underlying theme of pure geometry.This is no small feat. While the Romans built arches and domes, there is no evidence that they actually understood the principals behind it. They understood their proportional thickness to span and limits of scale only by the skillful and advanced use of a much simpler principal that they used in the absence of other scientific knowledge: trial and error. This might seem like an insult to their intelligence, but it isn’t. Using a proxy for an engineering concept that you don’t have control of in order to use it is a risky strategy requiring their best engineering skills to manage.
Moreover the risk of using and evidence-based/ trial-and-error based engineering concept was high for other reasons: embarrassment in the face of failure of whomever tries it, and the ire of the powerful patron who put their resources and trust in whomever did it. Slavery or even beheading would not have been becoming when you’re a well-respected Architect in the Roman Empire or Republic, I’m sure.
We see that they cast coffers into the dome to lighten it, but we don’t know if they put two-and-two together, and understood that the space in between them turned into ribs made stronger by tie-ing them together with the concentric rings formed by the horizontal elements between the coffers. It took several centuries before we saw any rib-vaults that represent historical evidence that building technology knew and understood the concept.
The trial-and-error issue extend to the material too: they “discovered” concrete in that they thought it could do something based on making mortar. Using volcanic ash, they produced a hydrating-lime concrete without really knowing that it was the hydration that was producing something like modern concrete. The invention of modern concrete is attributed to French gardener in the 2nd half the 19th century noodling around with a better way to make flower pots, and an Englishman who observed some of the hydrating and heat generating reaction of slack lime.
So the take-away from this is that skillful use of what you know in order to do more than you know isn’t just possible, but it creates the examples that other can “reverse engineer” to determine the unknown engineering principals themselves.
So there you have it – someone had to take a leap of faith – but the results for civilization was the ability to build more and better shelter using fewer resources, and this incrementally improved the lives of more people. This whole concept is lost on modern environmentalists whose luddite outlook is based on a are nostalgia of something that never existed, and is detrimental to the largest number of people. After all, if you tried to engage in such an experiment today, they would do whatever they could to stop it because of the risk and use of resources, and immediately vilify the chemistry involved in making it as a “poison” that will only serve to pollute streams and “make the rich richer.”