On the common parts of fortresses, which are 14. The less difficult and the more simple that which leads us to the desired end, the more powerful it should be reckoned. The members of fortresses are 18. Of which the first is a well or cistern, situated in the keep or in the castellan's room, so that he may take it from others and others may not take it from him. And it must have conduits through which it can reach the soldiers' rooms. The second is that there be the mill and the hand-mills for the powder for bombards. The third, that there be the oven, with the things necessary for baking bread. The fourth, that the way of relief be secure, and cannot be cut off without great difficulty. The fifth, that the castellan's tower be stronger and more eminent than the others, so that it can strike the rest of the fortress and not be struck. The sixth, that if several castellans are set in several towers within one and the same fortress, the ways of relief be so arranged that one castellan can neither bring in nor let out soldiers without the other castellan's leave. The seventh, that the fortress be of the smallest circuit possible, keeping due proportion. The eighth is that the walls of the circuit be high in themselves, but in a low place, and be scarped for two-thirds of their height, with the machicolations among the corbels. The ninth is that the towers be attached to the walls by themselves, or with angled wings of wall, of the height of the walls, with flanking fire. The tenth is that in front of the gate there be a ravelin, made in such a form that it strikes and cannot be struck, and provides a sufficient shield to the entrance of the keep. The eleventh is that the ditches be wide and deep, with high banks toward the bottom of the ditch. And on the outside let it be without hollows and oblique, so that the soldiers cannot make a shield of it against the fortress. The twelfth is that the entrances be reversed, with covered ways. The thirteenth is that the ditches be near. The fourteenth is that the dwellings of the household be built weakly within the circuit, in a place where they can easily be ruined from the principal tower. The fifteenth is that the towers be round, because a round form resists more and receives every impact less, and the walls angular and never round, because the fire of the towers that are to the flank uncovers little of that wall, on account of its curvature. Whence it would be necessary, if one wished one tower to defend the other, to make them close together, at great expense and little use. The sixteenth is that the angles [Continues on fol. 95 recto]