The Roman infantry, now stripped of protection on both its flanks, formed a wedge that drove deeper and deeper into the Carthaginian semicircle, driving itself into an alley formed by the African infantry on the wings.[33] At this decisive point, Hannibal ordered his African infantry to turn inwards and advance against the Roman flanks, creating an encirclement in one of the earliest known examples of a pincer movement.
When the Carthaginian cavalry attacked the Romans in the rear and the African flanking echelons assailed them on their right and left, the advance of the Roman infantry was brought to an abrupt halt. The Romans were enclosed in a pocket with no means of escape. The Carthaginians created a wall and began destroying them. Polybius wrote, "as their outer ranks were continually cut down, and the survivors forced to pull back and huddle together, they were finally all killed where they stood."[31]
As Livy described, "So many thousands of Romans were dying... Some, whom their wounds, pinched by the morning cold, had roused, as they were rising up, covered with blood, from the midst of the heaps of slain, were overpowered by the enemy. Some were found with their heads plunged into the earth, which they had excavated; having thus, as it appeared, made pits for themselves, and having suffocated themselves."[2]:22.51 Cowley claims that nearly six hundred legionaries were slaughtered each minute until darkness brought an end to the bloodletting.[34] Only 14,000 Roman troops managed to escape, most of whom had cut their way through to the nearby town of Canusium.