1. Those who have filled books of unusually large size, Emperor, in setting forth their intellectual ideas and doctrines, have thus made a very great and remarkable addition to the authority of their writings. I could wish that circumstances made this as permissible in the case of our subject, so that the authority of the present treatise might be increased by amplifications; but this is not so easy as it may be thought. Writing on architecture is not like history or poetry. History is captivating to the reader from its very nature; for it holds out the hope of various novelties. Poetry, with its measures and metrical feet, its refinement in the arrangement of words, and the delivery in verse of the sentiments expressed by the several characters to one another, delights the feelings of the reader, and leads him smoothly on to the very end of the work.

2. But this cannot be the case with architectural treatises, because those terms which originate in the peculiar needs of the art, give rise to obscurity of ideas from the unusual nature of the language. Hence, while the things themselves are not well known, and their names not in common use, if besides this the principles are described in a very diffuse fashion without any attempt at conciseness and explanation in a few pellucid sentences, such fullness and amplitude of treatment will be only a hindrance, and will give the reader nothing but indefinite notions. Therefore, when I mention obscure terms, and the symmetrical proportions of members of buildings, I shall give brief explanations, so that they may be committed to memory; for thus expressed, the mind will be enabled to understand them the more easily.

3. Furthermore, since I have observed that our citizens are distracted with public affairs and private business, I have thought it best to write briefly, so that my readers, whose intervals of leisure are small, may be able to comprehend in a short time.

Then again, Pythagoras and those who came after him in his school thought it proper to employ the principles of the cube in composing books on their doctrines, and, having determined that the cube consisted of 216[6] lines, held that there should be no more than three cubes in any one treatise.

4. A cube is a body with sides all of equal breadth and their surfaces perfectly square. When thrown down, it stands firm and steady so long as it is untouched, no matter on which of its sides it has fallen, like the dice which players throw on the board. The Pythagoreans appear to have drawn their analogy from the cube, because the number of lines mentioned will be fixed firmly and steadily in the memory when they have once settled down, like a cube, upon a man's understanding. The Greek comic poets, also, divided their plays into parts by introducing a choral song, and by this partition on the principle of the cubes, they relieve the actor's speeches by such intermissions.

5. Since these rules, founded on the analogy of nature, were followed by our predecessors, and since I observe that I have to write on unusual subjects which many persons will find obscure, I have thought it best to write in short books, so that they may the more readily strike the understanding of the reader: for they will thus be easy to comprehend. I have also arranged them so that those in search of knowledge on a subject may not have to gather it from different places, but may find it in one complete treatment, with the various classes set forth each in a book by itself. Hence, Caesar, in the third and fourth books I gave the rules for temples; in this book I shall treat of the laying out of public places. I shall speak first of the proper arrangement of the forum, for in it the course of both public and private affairs is directed by the magistrates.