Maybe an Ballista Tower.
Space: Only for one Bolt
Reloading Time: 10 sec
Range: shotrter than the Trebuche.
Cost: Depend of the Typ (Tower/ Field)
Aiming: Realslow
Special: Piercing like the 90 crossbow skill.
Bolt Weight: 100
Bolt Cost: 1 Buildinglog, 4 Metalbands, 4 Ingots,
Dmg: about 300 so they can kill Horse
Skill: 90 Siege to use