When Hasdrubal got word of the attack, he abandoned his position at 2 and brought his army back inside the city walls to counter the Romans, but they abandoned their positions the same night and retreated. The Romans overran the vacated position 2 and moved on to position 3 where they could devise an attack on the port. Meanwhile, parallel trenches were dug close to the city was with cross trenches connecting them. The trenches were filled with sharpened spikes.
Next, the Roman army began to construct a “mole” or sea wall to block the entrance to the commercial harbor (labeled 4). The mole was ninety six feet wide at the bottom, twenty-four feet wide at the surface, and constructed of heavy stones. The Roman army worked twenty-four hours a day on the construction until the mole was completed.