It seems, according to the historian Polybius, that the two walls built in front of this rampart were in accordance with the instructions of the “Treaty of fortifications of Philo” written towards the end of the 3rd century BC. J.-C. because with pétroboles (machines for throwing stones) and gantries (alleys covered in framework in the shelter of which the besieger walked towards the place) one easily carries simple walls. It is necessary to dig three ditches in front of the rampart; the first at a plethra (30 m), the next at 40 cubits (18.50 m) and the last at the same distance. These ditches must be more than 30 m wide and, with the earth removed, embankments are raised between them surmounted by a palisade which becomes a real stone wall for whoever is closest to the rampart. It is conceivable that such fortifications could never have been forced by the besiegers of Carthage.
Along the sea runs a simple enclosure wall whose limits are difficult to define exactly. It was to cover almost the entire peninsula. The city considers itself protected on this side by the rocky and very steep coast which constitutes a natural defence. Moreover, accustomed to mastering the seas, any dangerous attack, she thinks, will come from the land.
Carthage has two ports located in the southeastern part. Appian gives relatively precise descriptions of them. These are two artificial shelters located inside the enclosure. The northernmost, circular in shape, is the military port protected from prying eyes by a high and fortified wall, doubling the surrounding wall. It is dominated by the Admiral Palace which watches over the secrecy of military preparations and naval constructions.
Contiguous, towards the south, is located the merchant port probably rectangular, and much more accessible; on the seafront it is pierced with small canals, a frequent device to reduce the pressure due to the onslaught of the waves. Two artificial lagoons still exist today, northeast of Kram Bay. This commercial port commands the military port and its entrance is protected by a powerful fortified mole.
However, the consuls were in no hurry to begin hostilities. They are convinced that disarmed Carthage will be easy prey; they prefer to let tempers calm down and think that the city will eventually resign and obey. Moreover, the supply of the Roman army can only be done by the rallied maritime cities, Hasdrubal holding the countryside at the head of relatively large forces; Massinissa's attitude is not very encouraging either. Obviously, he had accepted the help of Rome for the sole purpose of seizing the Punic territory, but he now fears being robbed of the result acquired for the benefit of his powerful ally. To a request for troops, he replies haughtily:“I will send them when I judge that you need them. »