The Wall
The tower shield is not a shield that covers the fighter. The tower shield is a wall that the fighter hangs on. It is the shape of a door — the head plate at the top, the foot bar at the bottom — and the fighter behind it stands with both hands and gives up the rest of the fight. That is the whole argument: the fighter is not going anywhere. The line does not move. The line is the shield, and the shield is the line, and the fighter is the reason the line is made of something that thinks.
A journeyman tower shield is a frame of Iron and a face of boards, bound so the boards can split and the frame can hold them. A master tower shield has the head plate of Steel, and the head plate is the part that takes the blade. A masterwork tower shield is a story event, because the story has not yet written the one that stands behind it.
In the Hand
The tower shield is the third stance, made into a room: brace. The fighter behind it cannot run, cannot parry, and takes half the blunt wound into the frame instead of the body — but nothing behind the fighter takes anything at all, because the tower is the one who is hit. The tower shield is the reason a line of fighters is a line and not a crowd.
"A tower shield is a door that has decided to stay closed." — Rumzuck Umbatsch