The Carthaginian force lacks enough cavalry to contest both enemy wings symmetrically. Placing one flank against the walled town lets terrain and fortification substitute for mounted coverage. That frees the available cavalry to concentrate elsewhere and pursue a local advantage. The enemy's repeated movement from side to side shows the uncertainty created when a fixed obstacle changes the geometry of the line.
Notable Point · 1:28:11-1:28:35
A walled town anchors the flank that cavalry cannot cover
Unable to match enemy cavalry on both wings, the Carthaginian force uses the town wall to secure one side and concentrates mounted strength on the other.