Hannibal had for some time past pretended to be sick, to prevent the Romans from being surprised when they heard that he had spent such a long time in the same neighbourhood,
and he now pretended that his sickness was worse. His camp was distant three day's journey from Tarentum,
and when the time came he got ready a force of about ten thousand men selected from his infantry and cavalry for their activity and courage, ordering them to take provisions for four days;
and starting at dawn marched at full speed. Choosing about eighty of his Numidian horse he ordered them to advance in front of the force at a distance of about thirty stades and to spread themselves over the ground on each side of the road, so that no one should get a view of the main body,
but that of those whom they encountered, some should be made prisoners by them while those who escaped should announce in the town that a raid by Numidian horse was in progress.
When the Numidians were about a hundred and twenty stades away from the town, Hannibal halted for supper on the bank of a river which runs through a gorge and is not easily visible.
Here he called a meeting of his officers, at which he did not inform them exactly what his plan was, but simply exhorted them first to bear themselves like brave men, as the prize of success had never been greater, secondly to keep each of them the men under his command in close order on the march and severely punish all who left the ranks on no matter what pretext, and lastly to attend strictly to orders and to do nothing on their own initiative, but only what should be commanded.
After thus addressing and dismissing the officers, he started on his march just after dusk, intending to reach the walls of the town about midnight. He had Philemenus with him for a guide and had procured for him a wild boar to use in a manner that had been arranged.
Walbank Commentary