As for Siege System: Archery Towers are shit, they should be replaced by:
1) Loopholes/embrasures in Palisades/Brickwalls for defenders to shoot attackers using Bows/Slings while being protected themselves standing inside Palisades/Brickwalls.
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2) Burning Arrows (Arrow + Tar + Fire) for defenders to destroy Siege Engines by shooting through Loopholes/embrasures while being protected themselves standing inside Palisades/Brickwalls.