M. Vitruvius per Iocundum solito castigatior factus cum figuris et tabula ut iam legi et intelligi possit

A decorative initial "R" begins the text.
Reasoning, however, is that which demonstrates and is able to explain the constructed things by skill and the principle of proportion. Therefore, architects who have striven without literature, so as to be exercised in hands, have not been able to achieve the authority that they should have for their labors. Those, however, who have relied on reasoning and literature alone seem to have pursued the shadow and not the thing. But those who have learned both, as if armed with all weapons, have more quickly attained what was proposed with authority.

For in all things, but especially in architecture, these two are present: that which is signified, and that which signifies. The signified is the proposed matter about which one speaks. This is signified by a demonstration explained by the principles of the disciplines. Wherefore, he who professes himself an architect seems to need to be exercised in both parts. Therefore, it is necessary for him to be both gifted and teachable toward the discipline. For neither talent without discipline, nor discipline without talent, can make a perfect artist; and [he must be] literate, skilled in drawing, learned in geometry, not ignorant of optics, instructed in arithmetic, known in many histories, have diligently listened to philosophers, known music, not be ignorant of medicine, know the responses of legal consultants, and have known astrology and the principles of the sky.

The reasons why these must be so are these: It is necessary for an architect to know literature, so that he may be able to make his memory firmer with commentaries. Then, to have the knowledge of drawing, so that he may be more easily able to form the appearance of the work he wants with painted models. Geometry, however, provides many aids to architecture: and first, it teaches the use of the compass from straight lines: from which descriptions of buildings on sites are most easily expedited: the directions of squares, levels, and lines. Likewise, through optics, the lights of the sky are correctly led in buildings from certain regions. Through arithmetic, the expenses of buildings are calculated: the principles of measures are explained: and difficult questions of symmetries are found through geometric principles and methods. It is necessary to have known many histories, as architects often design many ornaments in works, about which they must render the reason to those asking why they have done so. For example, if someone has placed marble female statues in robes, which are called caryatides priestesses or women of Carya, instead of columns in a work, and has placed mutilated figures and crowns on their necks, he will render the reason to those inquiring thus: Carya, a city of the Peloponnese, conspired with the Persian enemies against Greece: afterwards, the Greeks, gloriously liberated from the war by victory, declared war on the Caryatids by common counsel. Thus, the town having been captured, the men killed, and the city destroyed, they led their matrons into slavery. They did not allow them to lay aside their robes or matronal ornaments: so that they would not lead them in one triumph, but that, pressed by grave humiliation as an eternal example of slavery, they might seem to pay the penalty for the city. Therefore, the architects who were there at that time designed their images in public buildings placed to carry the weight: so that even for posterity, the penalty of the Caryatids' sin might be handed down to memory.