From prescription, in the case of hypaethral edifices, open to the sky, in honor of Jupiter Lightning, the Heaven, the Sun, or the Moon: for these are gods whose semblances and manifestations we behold before our very eyes in the sky when it is cloudless and bright.

From food and water, then, we may learn whether sites are naturally unhealthy or healthy.

The Phrygians select a natural hillock, run a trench through the middle of it, dig passages, and extend the interior space as widely as the site admits. Over it they build a pyramidal roof of logs fastened together, and this they cover with reeds and brushwood, heaping up very high mounds of earth above their dwellings. Thus their fashion in houses makes their winters very warm and their summers very cool.

Geometry is of much assistance in architecture, and in particular it teaches us the use of the rule and compasses, by which especially we acquire readiness in making plans for buildings in their grounds, and rightly apply the square, the level, and the plummet. By means of optics the light in buildings can be drawn from fixed quarters of the sky. Difficult questions involving symmetry are solved by means of geometrical theories and methods.

Next I must tell about the machine of Ctesibius, which raises water to a height.

For we must not build temples according to the same rules to all gods alike, since the performance of the sacred rites varies with the various gods.

In fact, all kinds of men, and not merely architects, can recognize a good piece of work.