The idea is to add embrasures to palisades and brick walls:
1) Players standing at the inner side of the embrasure should be able to shoot a bow outside the palisade/brick wall to defeat besiegers.
2) Add possibility to craft flaming arrows (arrow + tar) to do huge damage to siege engines.
3) Change the usage of archery towers - instead of auto-shooting it should be used as follows: personage that climbed on archery tower significantly increases shooting distance. Archery towers now shouldnt decay over time.
4) And maybe that will be reasonable to add a 5% chance of critical distanse attack (one shot) - for noobs with primitive bows & arrows to be able to defend themselves against 1000+ stats players.