doric order, ancient rules restricted general proportions only, allowed individual flexibilty
On the origins of the architectural orders, which started with the Doric order: “if the Doric order could be attributed to an inventor, that inventor was a people among whom similar wants existed for a long period, and among whom a style of building was retained suitable to the climate and the habits of their life, and one which time slowly and gradually modified and brought to perfection, on principles rendered sacred by custom.”
The system of imitation in the Doric order was guided…“by the same principles which Nature herself adopts in her works, without the aid of which no bounds could have been set to the imagination and caprice of its improvers. In the copy no part can be said to be precisely similar to the model; the former displays sentiment, not calculation.
Proportions, and the rules necessary to be observed for the purpose of giving them elegance and effect, are only necessary to preserve uniformity in the principles on which we proceed, and for preventing too great a latitude of imagination in the productions of art.
We may be assured that whenever these become so fixed in any country, that its artists feel fettered by the restrictions which too rigid an adherence to ancient rules imposes, invention and taste are extinguished. The extraordinary difference which we find in the proportions and parts of the same order, plainly shews that the artists of Greece considered themselves only restricted in the general proportions.
from: A treatise on the decorative part of civil architecture, Volume 1 (Vitrivius) by Sir William Chambers, Joseph Gwilt, Thomas Hardwick