vigour.  In an attack by night on the suburb the Romans succeeded in passing from a tower—­placed in front of the walls and equal to them in height—­on to the battlements, and opened a little gate through which the whole army entered.  The Carthaginians abandoned the suburb and their camp before the gates, and gave the chief command of the garrison of the city, amounting to 30,000 men, to Hasdrubal.  The new commander displayed his energy in the first instance by giving orders that all the Roman prisoners should be brought to the battlements and, after undergoing cruel tortures, should be thrown over before the eyes of the besieging army; and, when voices were raised in disapproval of the act, a reign of terror was introduced with reference to the citizens also.  Scipio, meanwhile, after having confined the besieged to the city itself, sought totally to cut off their intercourse with the outer world.  He took up his head-quarters on the ridge by which the Carthaginian peninsula was connected with the mainland, and, notwithstanding the various attempts of the Carthaginians to disturb his operations, constructed a great camp across the whole breadth of the isthmus, which completely blockaded the city from the landward side.  Nevertheless ships with provisions still ran into the harbour, partly bold merchantmen allured by the great gain, partly vessels of Bithyas, who availed himself of every favourable wind to convey supplies to the city from Nepheris at the end of the lake of Tunes; whatever might now be the sufferings of the citizens, the garrison was still sufficiently provided for.  Scipio therefore constructed a stone mole, 96 feet broad, running from the tongue of land between the lake and gulf into the latter, so as thus to close the mouth of the harbour.  The city seemed lost, when the success of this undertaking, which was at first ridiculed by the Carthaginians as impracticable, became evident.  But one surprise was balanced by another.  While the Roman labourers were constructing the mole, work was going forward night and day for two months in the Carthaginian harbour, without even the deserters being able to tell what were the designs of the besieged.  All of a sudden, just as the Romans had completed the bar across the entrance to the harbour, fifty Carthaginian triremes and a number of boats and skiffs sailed forth from that same harbour into the gulf—­while the enemy were closing the old mouth of the harbour towards the south, the Carthaginians had by means of a canal formed in an easterly direction procured for themselves a new outlet, which owing to the depth of the sea at that spot could not possibly be closed.  Had the Carthaginians, instead of resting content with a mere demonstration, thrown themselves at once and resolutely on the half-dismantled and wholly unprepared Roman fleet, it must have been lost; when they returned on the third day to give the naval battle, they found the Romans in readiness.  The conflict came off