Battle Tactic: Flank Rolling Barrage
Arrange heavy troops in a row of squares as in the shield wall, but position javelin units to one flank, either behind or to the side of that flank, so that all their fire hits the opposing enemy flank only. As the javelins help to quickly defeat the enemy opposing the heavy legions on that flank, bring these heavy units forward against the flanks of the remaining enemy units. Reposition the javelins to fire on the next enemy unit along the line, until it too is driven off, and it's opposing heavy legion brought forward on the flank of the remaining enemy units. Repeat the process all along the enemy front, each sector in succession. You will quickly roll up the enemy front.
Key point: When you move your legion squares to attack the enemy, do so very lightly so they only contact the enemy with the edge of the square. If you push the attack too deeply, the square will crumple against the enemy units and loose it's formation integrity together with it's defensive advantages.