Walls, gates and the towers and galleries that defend them.
Wall Foundation Lifts walls, gatehouses, towers and hoardings over uneven ground, and stacks for a bigger rise. Can't be hit while something stands on it. 
Palisade A wall of sharpened logs that blocks the way for everyone. 
Wall A solid wall of iron-banded planks that blocks the way for everyone. 
Gatehouse A fortified gate with stairs up to the wall walk. Shuts when enemies or bandits come near. 
Drawbridge Gatehouse A gatehouse on a foundation, with a bridge two tiles out from its passage. The bridge raises when the gate shuts. Needs open space under the bridge. 
Log Hoarding A gallery on the wall where warriors roll logs down at enemies, knocking over everyone in their path. 
Oil Hoarding A gallery on the wall where warriors pour boiling canola oil on enemies below. 
Wall Tower Joins walls on any side and leads up to the wall walk. Sees far through the fog, further from high ground. 
Round Tower Taller than a wall tower, with an open top for a catapult, ballista or trebuchet. With a crew aboard, the machine on it shoots the nearest enemy in reach on its own. 
Blazer A fire basket on a wall, burning pine resin. Archers on the wall within two pieces of it shoot fire arrows at resin puddles. Now and then one gets burned. 
Resin Puddle Pine resin poured on the ground or a road. Archers by a lit Blazer set it alight with fire arrows. It burns for 6 hours and hurts everyone in it, your own too.