Quote Originally Posted by Sand
If the Romans chose to defend their city then Hannibal would not be able to take it with the forces available - he had to constantly move around Italy to plunder supplies to feed and pay his men. He did not have the logistical support from Carthage to sit in place for 6 or 7 months sieging the city.

Rome chose not to surrender and to keep fighting, and whilst they didnt have enough men under arms to fight a open battle they certainly had enough to secure Rome and hold off a direct assault so Hannibal never really had a chance of taking the city. There is the question of what the Roman reaction might have been if Hannibal had set out for Rome straight away - a massive, unprecedented Roman defeat and only a week later Hannibals army on your doorstep - but it would have been a bluff.

And it needs to be remembered that Cannae wasnt kind to Hannibal either - he lost over 4,500 men - over 10% of his force. It took them hours to kill all the trapped Romans and I doubt the army would have been in any shape to immediately force march to Rome in its aftermath.

As for the man power, Rome was frightening foe as countless other generals and kings would learn. In the immediate aftermath of Cannae they raised 14,000 volunteers from freed slaves and criminals who were granted freedom in exchange for service, equipped with weapons taken from temples and siezed from the gauls in past campaigns.

Only a short time after Cannae the Romans were able to a field an army of 25,000 men. The year after Cannae Rome was fielding 14 legions. 3 years after that, 25 legions.
Sand pretty much hit the nail on the head...

Hannibal was in no fit state to besiege Rome. He lacked the supply base (as most of the Roman Italians allies did not desert to Hannibal even after the victory at Cannae) to do so, and he lacked the manpower to storm the city...

The problems that a general/military encountered when besieging a city should not be underestimated. Often besieging a city took as heavy a toll on the besiegers (through disease, starvation), as on the besieged. For most of history, even the most powerful militaries were not able to besiege one major fortress/city a season, if the enemy had a similar level of technology, ohter than attempting to take the places by storm.