The battle opened, after preliminary skirmishing, with Hanni bal's order to the drivers of the elephants to charge the Roman line. Scipio promptly countered by a blast of trumpets along the whole line. The strident clamour so startled and terrified the elephants that many of them at once turned back on their own troops. This was especially the case on the left wing, where they threw the Numidians, Hannibal's best cavalry wing, into disorder just as they were advancing to the attack. Masinissa seized this golden opportunity to launch a counter-stroke, which inevitably overthrew the disorganized opponents. With Masinissa in hot pursuit, they were driven from the field, and so left the Carthaginian left wing exposed. The remainder of the elephants wrought much havoc among Scipio's velites, caught by their charge in front of the Roman line. But the foresight that had provided the "lanes" and laid down the method of withdrawal was justified by its results. For the elephants took the line of least resistance, penetrating into the lanes rather than facing the firm knit ranks of the heavy infantry maniples. Once in these lanes the velites who had retired into the lateral passages, between the lines, bombarded them with darts from both sides. Their reception was far too warm for them to linger when the door of escape was held wide open. While some of the elephants rushed right through, harmlessly, and out to the open in rear of the Roman army, others were driven back out of the lanes, and fled towards the Carthagin ian right wing. "It was at this moment that Laelius, availing him self of the disturbance created by the elephants, charged the Carthaginian cavalry, and forced them to headlong flight. He pressed the pursuit closely, as likewise did Masinissa." Both Han nibal's flanks were thus stripped bare.
In the meantime the infantry of both armies had slowly ad vanced on each other, except that Hannibal kept his third line back. At first the Gauls and Ligurians had the balance of advan tage, through their personal skill in skirmishing and more rapid movement. But the Roman line remained unbroken, and the weight of their compact formation pushed the enemy back despite losses. Another factor told, for while the leading Romans were encouraged by the shouts from the rear lines, coming on to back them up, Hannibal's second line—the Carthaginians—failed to support the Gauls, but hung back in order to keep their ranks firm. Forced steadily back, and feeling they had been left in the lurch by their own side, the Gauls turned about and fled. When they tried to seek shelter in the second line they were repulsed by the Carthaginians, who deemed it essential to avoid any disarray which might enable the Romans to penetrate their line. In a short time the relics of the first line had dispersed completely, or disappeared round the flanks of the second line. The latter, how ever, showed their fighting quality by thrusting back the Roman first line—the hastati. In this they were helped by a human obstacle, the ground encumbered with corpses and slippery with blood, which disordered the ranks of the attacking Romans. Even the principes had begun to waver when they saw the first line driven back so decisively, but their officers rallied them, and led them forward in the nick of time to restore the situation. This re inforcement was decisive. Hemmed in, because the Roman for mation produced a longer frontage and so overlapped their line, the Carthaginians were steadily cut to pieces. The survivors fled back on the relatively distant third line, but Hannibal continued his policy of refusing to allow the fugitives to mix with and dis turb an ordered line.
The curtain now rose on what was practically a fresh battle. The Romans "had penetrated to their real antagonists, men equal to them in the nature of their arms, in their experience of war, in the fame of their achievements. . . ." Livy's tribute is borne out by the fierceness and the long uncertain issue of the subsequent conflict, which refutes the suggestion that Hannibal's "Old Guard" was but a shadow of its former power—in the days of Trasimenus and Cannae. The Romans had the moral advantage of having
routed two successive lines, as well as the cavalry and elephants, but they had now to face a compact and fresh body of probably 24,000 veterans, under the direct inspiration of Hannibal. And no man in history has shown a more dynamic personality in infusing his own determination in his troops. The Romans, too, had at last a numerical advantage, not large, however—the forces were "nearly equal in numbers" according to Polybius—and in reality still less than it appeared. For while all Hannibal's third line were fresh, on Scipio's side only the triarii had not been engaged, and these represented but half the strength of the hastati or principes. Further, the velites had been so badly mauled that they had to be relegated to the reserve, and the cavalry were off the field, en gaged in the pursuit. Thus it is improbable that Scipio had at his disposal for this final blow more than 18,000 or 20,000 infantry, less the casualties these had already suffered.
His next step is characteristic of the man—of his cool calcula tion even in the heart of a battle crisis. He sounded the recall to his leading troops, and then, in face of an enemy at hardly more than a bow-shot distance, he not only reorganized his troops but reconstructed his dispositions. His problem was this : against the first two enemy lines the Roman formation, shallower than the Carthaginian phalanx and with intervals, had occupied a wider frontage, and so enabled him to overlap theirs. Now, against a body double the strength, his frontage was no longer, and perhaps less, than Hannibal's. His appreciation evidently took in this factor, and with it two others. First, that in order to concentrate his missile shock power for the final effort it would be wise to make his line as solid as possible and this could be done because there was no longer need for or advantage in retaining intervals be tween the maniples. Second, that as his cavalry would be return ing any moment there was no advantage in keeping the ortho dox formation in depth and using the principes and triarii as a di rect support and reinforcement to his front line. The blow should be as concentrated as possible in time and as wide as possible in striking force rather than a series of efforts. He, therefore, made his hastati close up to form a compact centre without intervals. Similarly he closed each half of his principes and triarii outwards, and moved them forward to extend the flank on either wing. He now once more overlapped the hostile front. The role of Scipio's infantry in the final phase was to fix Hannibal's force ready for the decisive manoeuvre to be delivered by the cavalry. For this role violence and wideness of onslaught was more important than sustenance. Scipio made his redistribution deliberately and un hurriedly—the longer he could delay the final tussle, the more time he gained for the return of his cavalry. It is not unlikely that Masinissa and Laelius pressed the pursuit rather too far, and so caused an unnecessary strain on the Roman infantry and on Scipio's plan. For Polybius tells us that when the rival infantries met, "the contest was for long doubtful, the men falling where they stood out of determination, until Masinissa and Laelius arrived providentially at the proper moment." Their charge, in the enemy's rear, clinched the decision, and though most of Hanni bal's men fought grimly to the end, they were cut down in their ranks. Of those who took to flight few escaped.
The completeness of the victory left no room for a strategic pursuit, but Scipio did not linger in developing the moral ex ploitation of his victory. An immediate move on Carthage achieved its object, a bloodless capitulation.