Alright, I have this scene, well two scenes in my head, one involving catapults/trebuchets and the other horses and I need some questions involving the certain physics to each concept. Catapults/Trebuchets Starting off here with Catapults and Trebuchets. Basically the scene I want to depict in the story is where an encroaching force (an army if you will) begins to invade from a mountain pass (a low pass in the mountain range with mountains on each side). I was thinking of a defense mechanism were projectiles would be flung to hit the surrounding mountains causing rocks and stones to fall initiating an avalanche to block the pass. Now the basic question here is what will be more realistic and/or cause the best effect. From what I researched Catapults are small-medium sized and use some type of elastic to fling the projectile whereas trebuchets are large in side and use a counterweight to fling the projectile. Which one will initiate an avalanche to block the pass? If is trebuchet would it be too large? And if it is catapult, can it even shoot that high with enough force? Horses Second concept is horses. I just need some realistic physics here. Think Peter Jackson's Lord of the Rings the Two Towers movie where Gandalf and Eomer charge down horseback to liberate Helm's Deep. Obviously this is unrealistic as cliff is too steep and the degree of the angle would either slow the horses to canter down or make them trip over themselves causing massive fail. What I need here is what is the maximum degree of angle which horses can sprint/gallop down from a hill. I plan to use this regarding a scene-in-progress which I will later work on.