Defense units
Right I gonna list here what the defense unit is and what they do. Don't really have access to the material right now so here's what I can say.
Rolling stones, and logs are used to attack the invading troops.
Traps detain them. So if you have 1k army attacking and have 100 traps, 100% working you'll end up with an attack force of 900 hitting you. So it's pretty useless, especially when battering rams come into play.
Blindages boost Archer defense.