Place the line in three ranks. The front rank stays tight, every man’s shield touches the neighbour’s shield on the left and right. In the second rank each man steps back just enough that his shield overlaps the two shields in front of him, covering any gaps. The third rank is more flexible – men can shift slightly to the left to compensate for any exposed angle. Use slightly larger shields on the left flank so the first man can block more of the angle, then the next man’s shield covers his left side. Have the leftmost man in each rank stand a few centimetres taller or with a larger shield, creating a “bump” that deflects the enemy’s spear thrusts. Keep the spacing uniform: about 30‑cm between men in the front rank, 45‑cm in the back rank. In training, have them practice stepping in synchrony, so the front line moves as one unit, and the second rank follows the same rhythm, creating a seamless wall that closes any flank gaps.

Excellent, keep the cadence tight, no gaps, refine until it’s muscle memory, and the front line will be an unbreachable wall.