|Rome's San Sebastian Gate|
Roman women appealed to the gods by sweeping the floors of their temples with their hair.
The miracle happened: Hannibal turned away.
As Livy records in Ab Urbe Condita (The History of Rome) Book 22.51,
"...Hannibal's officers all surrounded him and congratulated him on his victory, and urged that after such a magnificent success he should allow himself and his exhausted men to rest for the remainder of the day and the following night. Maharbal, however, the commandant of the cavalry, thought that they ought not to lose a moment. 'That you may know', he said to Hannibal, 'what has been gained by this battle I prophesy that in five days you will be feasting as victor in the Capitol. Follow me; I will go in advance with the cavalry; they will know that you are come before they know that you are coming.' To Hannibal the victory seemed too great and too joyous for him to realise all at once. He told Maharbal that he commended his zeal, but he needed time to think out his plans. Maharbal replied: "The gods have not given all their gifts to one man. You know how to win a victory, Hannibal, you do not know how to use it.
That day's delay is believed to have saved the City and the empire."
So, was Maharbal right?
The story, whether partly or wholly fanciful, is certainly well-expressed in dramatic fashion. However, Polybius, our more reliable source (for the most part), makes no mention of Maharbal in his account of Cannae; he mentions Maharbal commanding at Lake Trasimene over a year earlier, as well as the subsequent cavalry action around modern Assisi, about fifteen miles SE of Trasimene. Polybius tells us one Hasdrubal (the left wing of the army) and one Hanno (on the right) were the primary cavalry commanders at Cannae.
Sir Basil Henry Liddell Hart, from Pg. 12 of his Scipio Africanus: Greater Than Napoleon, with regards as an error the failure to pursue and destroy the contingent of 4,200 Roman fugitives after Cannae, who escaped form the larger Roman camp and...
"...made their way to Canusium. Their situation was still perilous, for this place lay only some four miles distant, and why Hannibal did not follow up his success by the destruction of this remnant, isolated from succor, remains one of the enigmas of history, to all appearance a blemish on his generalship..."
True, if the 10,000 total Romans who made it to Canusium (another 4,500 plus 50 cavalry with Varro made it to Venusia) had been rounded up, they wouldn't have been available for Marcus Marcellus to incorporate into his own standards later on.
But Hannibal did assault the smaller Roman camp with 7,000 men, who surrendered quickly; surrender was soon followed by the larger camp (though with a lesser amount of 5,800 upon surrender). Besieging Canusium with 10,000 Roman troops soon holding it could have taken weeks, even months.
Hannibal and his officers had swiftly rounded up altogether 18,700 prisoners from different points: Livy convincingly tells us that 10,000 men escaped to the larger camp, 7,000 to the smaller, and 2,000 to Cannae itself, which had no fortifications for protection from the lieutenant Carthalo and his pursuing cavalry (Book 22.49); on the battlefield 4,500 men were taken, of which 1,500 were cavalry. Again, Hannibal took the smaller Roman camp, building an earthwork in the process that cut the besiged from the Aufidus, effectuating their near-immediate capitulation (these men were demoralized and fatigued beyond what most survivors of such a catastrophe to their side have ever experienced in war). But Livy tells us a little later that 600 broke out in a brave sortie (Book 22.60); again, of the 10,000 in the larger camp, 4,200 made their escape to Canusium.
Moreover, immediately following the Battle of Cannae, Hannibal learned he had lost many of his most senior and experienced officers. A period of consolidation was now required, and, of no minor importance, the battlefield was was covered with vast amounts of booty and military equipment - the very essentials behind the financing of his war. This bore very real implications; his soldiery were mainly mercenaries, and they had served him with the utmost vigor and loyalty, and it was primarily the prospect of booty that drove them to serve with him. They now deserved their moment of reward. He couldn't refuse them.
So, rather than attack Rome and confront the two armies that Rome had placed before him, Hannibal decided to burn the nearby countryside and withdraw to fight elsewhere.
It seems that Hannibal was not equipped to lay siege to Rome anywat. Instead he was trying to wear Rome down with a war of attrition. He continued to destroy Italian lands and to destroy villages that his forces could not hold.
Using the same 'scorched earth' strategy - to starve Hannibal's forces - the Romans burnt crops and building in front of Hannibal's advancing army, and they moved people from the countryside to towns. The Romans also took their revenge by plundering towns they believed had befriended Hannibal and beheading men they believed had fought on the side of Carthage.