The stone in quarries is found to be of different and unlike qualities. In some it is soft, in others it is medium, in still others it is hard as in lava quarries. There are also numerous other kinds: for instance, in Campania, red and black tufas; in Umbria, Picenum, and Venetia, white tufa which can be cut with a toothed saw like wood.

In all matters but particularly in architecture, that which is signified is the subject of which we may be speaking and that which gives significance is a demonstration on scientific principles. One who professes himself an architect should be well versed in both directions.

For not all things are practicable on identical principles

I, therefore, O Caesar, do not publish this work, merely prefixing my name to a treatise which of right belongs to others, nor think of acquiring reputation by finding fault with the works of any one.

Pytheos made a mistake by not observing that the arts are each composed of two things, the actual work and the theory of it. One of these, the doing of the work, is proper to men trained in the individual subject, while the other the theory is common to all scholars.

Music, also, the architect ought to understand so that he may have knowledge of the canonical and mathematical theory, and besides be able to tune ballistae , catapultae, and scorpiones to the proper key. For to the right and left in the beams are the holes in the frames through which the strings of twisted sinew are stretched by means of windlasses and bars, and these strings must not be clamped and made fast until they give the same correct note to the ear of the skilled workman.

Astronomers have a common ground for discussion with musicians in the harmony of the stars and musical concords in tetrads and triads of the fourth and the fifth, and with geometricians in the subject of vision; and in all other sciences many points, perhaps all, are common so far as the discussion of them is concerned. But the actual undertaking of works which are brought to perfection by the hand and its manipulation is the function of those who have been specially trained to deal with a single art.