The battering ram, the most basic of siege weapons, was used in close quarters by groups of men to break through vulnerable defenses, particularly doors and gates. Often a battering ram was simply a large tree that had been cut down with branches removed. Because soldiers manning the ram tended to be highly vulnerable, more advanced models had wooden structures to protect the ram operators. Battering rams were also at times set on wheels, or used as a part of siege towers.
Siege towers were wooden towers built to help soldiers surmount fortified walls. A siege tower was usually rectangular, at least the same height as the wall being attacked, and set on four wheels. As the tower was rolled up to the walls, archers could be stationed inside to fire inside the castle or fort. Siege towers were sometimes covered in animal hides to protect them from fire.
Catapults, which hurled projectiles over long distances, evolved into many different forms through the history of siege warfare. The first catapults developed out of the Roman balista, which was essentially a very large crossbow. With a tension catapult, a rope was pulled back under tension, and used energy from the tension release to throw the projectile. A torsional catapult utilized a swinging arm. The mangonel was a type of torsion catapult that could send objects over 1,000 feet in distance. An onager was another type of torsion catapult that used twisting ropes to store energy.
The trebuchet was an advanced catapult that used gravity to propel objects. Trebuchets tended to be very large, and were composed of a lever and a sling. A heavy weight was suspended from the shorter end of the lever, with the sling at the end of the longer arm. Attackers could equip the sling with stones as large as 200 pounds. Pulling back the sling would lift the weight. Releasing the sling would cause the weight to drop, throwing the weapon's payload in the process. Trebuchets were able to send objects over several hundred yards.