Scipio now resolved on making a great counter-move--he would block up the approach to the harbour. He had, in fact, for some time past foreseen the necessity of taking this step, and had prepared a vast amount of material for the work, employing great numbers of the native population in quarrying stone and cutting timber. So much had been accomplished in this way that when the time came for executing the work little more than the actual construction remained to be done. This was not so difficult as it had seemed. The harbour mouth was not very far from the shore occupied by the Romans.
The first thing was to lay a foundation for the mole that it was proposed to build. This was done by sinking huge blocks of roughly-hewn stone, chiefly during moonless nights. During this stage of the work the besieged took little heed of what was going on, or, anyhow, took no pains to interrupt or hinder it. There was a suspicion, and more than a suspicion, of Scipio's purpose, but Hasdrubal, himself indolent and incompetent, haughtily refused to listen to any suggestion from his subordinates. But even Hasdrubal was roused when the structure reached the surface of the water. What he saw was a mole, more than thirty yards broad, stretching across the mouth of the harbour, and shutting off every channel available even for the smallest craft.
Hasdrubal now developed, or accepted, a plan which for a time at least was a virtual check to Scipio's move. He kept up a brisk discharge of missiles on the men employed in building the mole. So sharp and continuous was it that the besiegers had little attention to give to what was being done on the opposite side of the harbour. It was a surprise, and a very unwelcome surprise to them, that no sooner had they stopped up one mouth of the harbour, than they found that another exit had been created. The whole population, every man, woman, and child in the city, that could ply a spade or a pick, wheel a barrow-load or carry a basket of earth, had been working night and day at excavating another mouth to the harbour.
Nor was this all; a still greater surprise, so great, indeed, as to be almost overwhelming, remained behind.
One of the conditions of the peace granted to Carthage after the fatal defeat of Zama[37] had been the surrender of all the ships of war but twenty. In a way this condition had been observed. There had never been more than twenty ships in commission at one time; but the old hulks had not always been destroyed. At first they had been kept to serve various purposes; latterly, as another war began to loom in the future, they had been preserved with the intention of using them again. A number of merchant vessels also were furnished with crews and an armament that was at least passably effective.