Of these methods of attack, the first, wherein the city was entirely surrounded, exposed the defenders to more sudden perils and left them more doubtful remedies. For while it was necessary for them to have a sufficient force at all points, it might happen that the forces at their disposal were not numerous enough to be everywhere at once, or to relieve one another. Or if their numbers were sufficient, they might not all be equally resolute in standing their ground, and their failure at any one point involved a general defeat. Consequently, as I have said, this method of attack was often successful. But when it did not succeed at the first, it was rarely renewed, being a method dangerous to the attacking army, which having to secure itself along an extended line, was left everywhere too weak to resist a sally made from the town; nay, of itself, was apt to fall into confusion and disorder. This method of attack, therefore, could be attempted once only and by way of surprise. Against breaches in the walls the defence was, as at the present day, to throw up new works; while mines were met by counter-mines, in which the enemy were either withstood at the point of the sword, or baffled by some other warlike contrivance; as by filling casks with feathers, which, being set on fire and placed in the mine, choked out the assailants by their smoke and stench. Where towers were employed for the attack, the defenders sought to destroy them with fire; and where mounds of earth were thrown up against the walls, they would dig holes at the base of the wall against which the mound rested, and carry off the earth which the enemy were heaping up; which, being removed from within as fast as it was thrown up from without, the mound made no progress. None of these methods of attack can long be persisted in and the assailant, if unsuccessful, must either strike his camp and seek victory in some other direction, as Scipio did when he invaded Africa and, after failing in the attempt to storm Utica, withdrew from his attack on that town and turned his strength against the Carthaginian army in the field; or else recourse must be had to regular siege, as by the Romans at Veii, Capua, Carthage, Jerusalem, and divers other cities which they reduced in this way.