The years of 149-148 B.C, were unsuccessful from the Roman standpoint as multiple attempts to assault the city failed. Then, after Scipio Aemilianus was elected consul in late 148, he proceeded to Carthage intent on finishing the war. Aemilianus spent the summer of 147 B.C. getting his army in shape and then in the fall built a double wall 3.2 miles across the Isthmus separating the city of Carthage from the rest of the Tunisian Peninsula. The inner wall would starve the Carthaginians into submission while the outer wall served to protect the Roman army from being attacked from behind. The inner wall was twelve feet high with parapets and towers. A central tower was high enough to provide a view into the city.
To help you understand the geography involved in this battle, I have constructed the following map which shows the city of Carthage and its critical landmarks.