5When we are satisfied with the spot fixed on for the site of the city, as well in respect of the goodness of the air as of the abundant supply of provisions for the support of the population, the communications by good roads, and river or sea navigation for the transport of merchandise, we should take into consideration the method of constructing the walls and towers of the city. Their foundations should be carried down to a solid bottom, if such can be found, and should be built thereon of such thickness as may be necessary for the proper support of that part of the wall which stands above the natural level of the ground. They should be of the soundest workmanship and materials, and of greater thickness than the walls above.
2From the exterior face of the wall towers must be projected, from which an approaching enemy may be annoyed by weapons, from the embrasures of those towers, right and left. An easy approach to the walls must be provided against: indeed they should be surrounded by uneven ground, and the roads leading to the gates should be winding and turn to the left from the gates. By this arrangement, the right sides of the attacking troops, which are not covered by their shields, will be open to the weapons of the besieged. The plan of a city should not be square, nor formed with acute angles, but polygonal; so that the motions of the enemy may be open to observation. A city whose plan is acute-angled, is with difficulty defended; for such a form protects the attacker more than the attacked.
3The thickness of the walls should be sufficient for two armed men to pass each other with ease. The walls ought to be tied, from front to rear, with many pieces of charred olive wood; by which means the two faces, thus connected, will endure for ages. The advantage of the use of olive is, that it is neither affected by weather, by rot, or by age. Buried in the earth, or immersed in water, it lasts unimpaired: and for this reason, not only walls, but foundations, and such walls as are of extraordinary thickness, tied together therewith, are exceedingly lasting.
4The distance between each tower should not exceed an arrow’s flight; so that if, at any point between them, an attack be made, the besiegers may be repulsed by the scorpions and other missile engines stationed on the towers right and left of the point in question. The walls will be intercepted by the lower parts of the towers where they occur, leaving an interval equal to the width of the tower; which space the tower will consequently occupy: but the communication across the void inside the tower, must be of wood, not at all fastened with iron: so that, if the enemy obtain possession of any part of the walls, the wooden communication may be promptly cut away by the defenders, and thus prevent the enemy from penetrating to the other parts of the walls without the danger of precipitating themselves into the vacant hollows of the towers.
5The towers should be made either round or polygonal. A square is a bad form, on account of its being easily fractured at the quoins by the battering-ram; whereas the circular tower has this advantage, that, when battered, the pieces of masonry whereof it is composed being cuneiform, they cannot be driven in towards their centre without displacing the whole mass. Nothing tends more to the security of walls and towers, than backing them with walls or terraces: it counteracts the effects of rams as well as of undermining.
6It is not, however, always necessary to construct them in this manner, except in places where the besiegers might gain high ground very near the walls, from which, over level ground, an assault could be made. In the construction of ramparts, very wide and deep trenches are to be first excavated; the bottom of which must be still further dug out, for receiving the foundation of the wall. This must be of sufficient thickness to resist the pressure of the earth against it.
7Then, according to the space requisite for drawing up the cohorts in military order on the rampart, another wall is to be built within the former, towards the city. The outer and inner walls are then to be connected by cross walls, disposed on the plan after the manner of the teeth of a comb or of a saw, so as to divide the pressure of the filling in earth into many and less forces, and thus prevent the walls from being thrust out.
8I do not think it requisite to dilate on the materials whereof the wall should be composed; because those which are most desirable, cannot, from the situation of a place, be always procured. We must, therefore, use what are found on the spot; such as square stones, flint, rubble stones, burnt or unburnt bricks; for every place is not provided, as is Babylon, with such a substitute for lime and sand as burnt bricks and liquid bitumen; yet there is scarcely any spot which does not furnish materials whereof a durable wall may not be built.