1. The Greeks lay out their forums in the form of a square surrounded by very spacious double colonnades, adorn them with columns set rather closely together, and with entablatures of stone or marble, and construct walks above in the upper story. But in the cities of Italy the same method cannot be followed, for the reason that it is a custom handed down from our ancestors that gladiatorial shows should be given in the forum.

Forum At Timgad
From Gsell
forum at timgad
A, Forum. B, Basilica. C, Curia. C', Official Building. D, Small Temple. E, Latrina. F, Atrium.

2. Therefore let the intercolumniations round the show place be pretty wide; round about in the colonnades put the bankers' offices; and have balconies on the upper floor properly arranged so as to be convenient, and to bring in some public revenue.

The size of a forum should be proportionate to the number of inhabitants, so that it may not be too small a space to be useful, nor look like a desert waste for lack of population. To determine its breadth, divide its length into three parts and assign two of them to the breadth. Its shape will then be oblong, and its ground plan conveniently suited to the conditions of shows.

3. The columns of the upper tier should be one fourth smaller than those of the lower, because, for the purpose of bearing the load, what is below ought to be stronger than what is above, and also, because we ought to imitate nature as seen in the case of things growing; for example, in round smooth-stemmed trees, like the fir, cypress, and pine, every one of which is rather thick just above the roots and then, as it goes on increasing in height, tapers off naturally and symmetrically in growing up to the top. Hence, if nature requires this in things growing, it is the right arrangement that what is above should be less in height and thickness than what is below.

4. Basilicas should be constructed on a site adjoining the forum and in the warmest possible quarter, so that in winter business men may gather in them without being troubled by the weather. In breadth they should be not less than one third nor more than one half of their length, unless the site is naturally such as to prevent this and to oblige an alteration in these proportions. If the length of the site is greater than necessary, Chalcidian porches may be constructed at the ends, as in the Julia Aquiliana.

5. It is thought that the columns of basilicas ought to be as high as the side-aisles are broad; an aisle should be limited to one third of the breadth which the open space in the middle is to have. Let the columns of the upper tier be smaller than those of the lower, as written above. The screen, to be placed between the upper and the lower tiers of columns, ought to be, it is thought, one fourth lower than the columns of the upper tier, so that people walking in the upper story of the basilica may not be seen by the business men. The architraves, friezes, and cornices should be adjusted to the proportions of the columns, as we have stated in the third book.

Forum At Pompeii
From Mau
forum at pompeii
A, Forum. B, Basilica. C, Temple of Apollo. D, D', Market Buildings. E, Latrina. F, City Treasury. G, Memorial Arch. H, Temple of Jupiter. I, Arch of Tiberius. K, Macellum (provision market). L, Sanctuary of the City Lares. M, Temple of Vespasian. N, Building of Eumachia. O, Comitium. P, Office of the Duumvirs. Q, The City Council. R, Office of the Aediles.

Plan Of The Basilica At Pompeii
From Durm
plan of the basilica at pompeii

6. But basilicas of the greatest dignity and beauty may also be constructed in the style of that one which I erected, and the building of which I superintended at Fano. Its proportions and symmetrical relations were established as follows. In the middle, the main roof between the columns is 120 feet long and sixty feet wide. Its aisle round the space beneath the main roof and between the walls and the columns is twenty feet broad. The columns, of unbroken height, measuring with their capitals fifty feet, and being each five feet thick, have behind them pilasters, twenty feet high, two and one half feet broad, and one and one half feet thick, which support the beams on which is carried the upper flooring of the aisles. Above them are other pilasters, eighteen feet high, two feet broad, and a foot thick, which carry the beams supporting the principal raftering and the roof of the aisles, which is brought down lower than the main roof.

7. The spaces remaining between the beams supported by the pilasters and the columns, are left for windows between the intercolumniations. The columns are: on the breadth of the main roof at each end, four, including the corner columns at right and left; on the long side which is next to the forum, eight, including the same corner columns; on the other side, six, including the corner columns. This is because the two middle columns on that side are omitted, in order not to obstruct the view of the pronaos of the temple of Augustus (which is built at the middle of the side wall of the basilica, facing the middle of the forum and the temple of Jupiter) and also the tribunal which is in the former temple, shaped as a hemicycle whose curvature is less than a semicircle.

Vitruvius' Basilica At Fano
vitruvius' basilica at fano

vitruvius' basilica at fano

8. The open side of this hemicycle is forty-six feet along the front, and its curvature inwards is fifteen feet, so that those who are standing before the magistrates may not be in the way of the business men in the basilica. Round about, above the columns, are placed the architraves, consisting of three two-foot timbers fastened together. These return from the columns which stand third on the inner side to the antae which project from the pronaos, and which touch the edges of the hemicycle at right and left.

9. Above the architraves and regularly dispersed on supports directly over the capitals, piers are placed, three feet high and four feet broad each way. Above them is placed the projecting cornice round about, made of two two-foot timbers. The tie-beams and struts, being placed above them, and directly over the shafts of the columns and the antae and walls of the pronaos, hold up one gable roof along the entire basilica, and another from the middle of it, over the pronaos of the temple.

10. Thus the gable tops run in two directions, like the letter T, and give a beautiful effect to the outside and inside of the main roof. Further, by the omission of an ornamental entablature and of a line of screens and a second tier of columns, troublesome labour is saved and the total cost greatly diminished. On the other hand, the carrying of the columns themselves in unbroken height directly up to the beams that support the main roof, seems to add an air of sumptuousness and dignity to the work.