The following is a summary i did on an essay i found on the internet. I wish i had more time to follow my passion. originall essay can be found at www.roman-empire.net
The newly elected Roman Consuls, Gaius Terentius Varro and Lucius Aemilius Paullus, who had both run on a platform of taking the war to Hannibal, were anxious to begin their tenure with military achievement. Hannibal meanwhile, still attempting to subvert Roman authority in the allied areas of Italy, was waiting for the Roman with approximately 40,000 men; Gauls, Carthaginians and Numidian cavalry. Hannibal, despite his numerical inferiority had such an overwhelming strategic edge, that he was eager to meet the new Roman challenge. Theoretically, the Roman tactic of crushing Hannibal between two large armies should have spelled his doom, but Hannibal's brilliance allowed him to turn the tables once the engagement got under way.
The Consul Varro was in command on the first day for the Romans, as the consuls alternated commands as they marched. Hasdrubal, commanding the Numidians, quickly overpowered the inferior Romans on the right flank and routed them. As Hasdrubal was routing the Roman horse, the mass of infantry on both sides advanced towards each other in the middle of the field. The Iberian and Gallic Celts on the Carthaginian side, while fierce, were no match for Roman armament and close-quartered combat. The Romans soon found that their success in the middle was pushing them into a potential disaster. Just as the Romans were on the brink of crushing the enemy center, the Carthaginian flanks were brought to bear and the pressure pinned in the Roman advance. Hasdrubals' cavalry completed the circle by forcing the rear of the Roman line to turn back and form a square. All around, the massive bulk of the Roman army was forced into confined space. Unable to continue the original break through against the Celts in the center of Hannibal's lines, the Romans were easy prey for the Carthaginians. Hannibal, with complete fury, encouraged his own men, under fear of the lash, if they weren't zealous enough in the slaughter.
Hannibal, however, still trying to win the hearts of the Italian Roman allies, once again released the prisoners, much to the dismay of his commanders. In salute to the fallen Paullus, Hannibal also honored him with ceremonial rituals in recognition of his valiant actions.
In the end, perhaps only as many as 15,000 Romans managed to escape with Varro. There was nothing keeping Hannibal from sacking Rome itself at this point, other than Hannibal. Still believing he couldn't take Rome itself, he preferred his strategy of pursuing revolt among the Roman allies.
Shortly after Cannae, the Romans rallied back, declaring full mobilization. As the land owning population was heavily diminished by losses to Hannibal, the Romans took advantage of the masses. In so doing, the Romans also refused to pay ransoms to Hannibal for any captured legionaries who still remained. While fortune would still be with Hannibal for some time, the war of attrition would only benefit Rome


