Such being the situation of the place, the Roman camp was protected on its inner side without any fortification by the lagoon and by the outer sea.
The intervening space, which connects the city with the mainland and which lay in the middle of his camp, was also left unintrenched by Scipio,
either to intimidate the enemy or to adapt it to his own particular purpose, so that there should be no impediment to sorties from his camp and subsequent retirement into it.
The circumference of the city was formerly not more than twenty stades — I am quite aware that many state it to be forty, but this is not true, as I speak not from report but from my own careful observation — and at the present day it has still further shrunk.
Scipio, then, when the fleet arrived in due time, decided to call a meeting of his troops and address them, using no other arguments than those which had carried conviction to himself and which I have above stated in detail.
After proving to them that the project was feasible, and pointing out briefly what loss its success would entail on the enemy and what an advantage it would be to themselves, he went on to promise gold crowns to those who should be the first to mount the wall and the usual rewards to such as displayed conspicuous courage.
Finally he told them that it was Neptune who had first suggested this plan to him, appearing to him in his sleep, and promising that when the time for the action came he would render such conspicuous aid that his intervention would be manifest to the whole army.
The combination in this speech of accurate calculation, of the promise of gold crowns, and therewithal of confidence in the help of Providence created great enthusiasm and ardour among the lads.
Walbank Commentary