Page:Vitruvius the Ten Books on Architecture.djvu/43

. V] done, the enemy will not be able to make his way to the other towers and the rest of the wall unless he is ready to face a fall.

5. The towers themselves must be either round or polygonal. Square towers are sooner shattered by military engines, for the



battering rams pound their angles to pieces; but in the case of round towers they can do no harm, being engaged, as it were, in driving wedges to their centre. The system of fortification by wall and towers may be made safest by the addition of earthen ramparts, for neither rams, nor mining, nor other engineering devices can do them any harm.

6. The rampart form of defence, however, is not required in all places, but only where outside the wall there is high ground from