From firmus (“stable, strong, firm; steadfast, true”).
Hellenistic: Constancy, firmness, stability, solidity
standing fast, firm, fixed
(of weather) steady, settled (of speech) calm, deliberate
First Principle or Firmitas
I believe that Vitruvius pointed out that styles change, but underneath each iteration of change, needs to have firm design. This principle is better understood when sculpting in stone. A principle hard for the clay modeler to understand.More on Richard Boyle
Richard Boyle interpreted Vitruvius Firmitas as Firmness