‘COMPANY HALT! These big bad dudes should be the heart of your army and a major part of your defense. They are very slow because they have all that armor but are perfect for hand to hand melee activity. If you have javelins they should be behind these moving walls
They patrol the walls waiting for a barbarian to get within their site and then throw deadly pilas, roman javelins. They patrol double walls near the towers. They also man the balistas that can be fired from a large bow at the top of the tower. One strike from a balista can kill a man easily.