Wall
Wall refers to the protective fortifications around towns in a siege. Building a Fort adds walls around the town, and then a Castle strengthens them to fortified walls. Building a Citadel has no effect on walls - it only adds main Arrow Tower to fortifications. Town walls block the movement of ground walking creatures and hamper the attacks of ranged attackers by 50%. Walls can be damaged and destroyed with Catapults, Cannons (with HotA) 
or Earthquake spell. Additionally, cyclopses and cyclops kings have the special ability to attack walls during a siege.
On the battlefield walls fill up 11 hexes, and 6 of them are indestructible. Wall hexes are divided into:
W hexes: 6 indestructible segments
(1) hex: Upper Wall
(2) hex: Mid-Upper Wall
(3) hex: Mid-Lower Wall
(4) hex: Lower Wall
(D) hex: Drawbridge
Destructible wall segments have 2 hitpoints (3 with Castle built), except Drawbridge which always has 2 hitpoints. The drawbridge can be opened by the town defenders, but not by attackers. However, if a stack dies while standing on the open drawbridge, it will not close.
During a siege hero forces can move only onto destructible wall hexes after destroying them.