Propriety is that perfection of style which comes when a work is authoritatively constructed on approved principles. It arises from prescription, from usage, or from nature.

There are two styles of walls "opus reticulatum," now used by everybody and the ancient style called "opus incertum." Of these, the reticulatum looks better, but its construction makes it likely to crack. On the other hand, in the opus incertum, the rubble lying in courses and imbricated, makes a wall which though not beautiful, is stronger.

In Sparta, paintings have been taken out of certain walls by cutting through the bricks, then have been placed in wooden frames, and so brought to the Comitium to adorn the aedileship of [C. Visellius] Varro and [C. Licinius] Murena.

The design of a temple depends on symmetry, the principles of which must be most carefully observed by the architect.

The oak has not the efficacy of the fir, nor the cypress that of the elm.

Remembering that Eratosthenes of Cyrene, employing mathematical theories and geometrical methods, discovered from the course of the sun, the shadows cast by an equinoctial gnomon, and the inclination of the heaven that the circumference of the earth is two hundred and fifty-two thousand stadia, that is, thirty-one million five hundred thousand paces.

Philosophy treats of physics where a more careful knowledge is required because the problems which come under this head are numerous... So the reader of Ctesibius or Archimedes and the other writers of treatises of the same class will not be able to appreciate them unless he has been trained in these subjects by the philosophers.