Tools of the Siege
When the Romans sieged an enemy, they didn't just wait around for the enemy to starve to death, as the enemy could have a large supply of food and water. Instead they used huge siege engines to attack the defenses of the besieged fort or city.
One of these engines, the onager, was very similar to most people's conception of a catapult. It consisted of a fixed base, and an arm that was wound in twined hair or sinew. This rope provided the torsion for throwing the projectile. A small sling was placed at the end of the arm, and a payload in that. The payload was usually a large stone ball, but could be a number of things, including skulls of the enemy. Onager means "donkey," and the weapon was so named because of it's incredible kickback. One tale features an engineer who was too close to an onager when it fired, and was reduced to a pulp.
Another weapon was the "scorpion," which worked like a fixed crossbow, and threw large javelins. This weapon was feared for it's accuracy, and it could be used to pick troops off walls. However, its more famous relative is the ballista, which was a large crossbow-type weapon that could hurl a 50-pound stone over 500 meters. A large ballista could be over 6 meters tall.
Also famous was the siege tower. This was a large, mobile tower that could be rolled up to the enemy's walls, and a drawbridge lowered from the top to allow soldiers access to the besieged fortress. These towers were covered in hide or armor, and had a full complement of archers to pick defenders off the ramparts. If the siege tower could not access the enemy because of adverse terrain, the Romans would simply build a ramp, or fill in a valley. Time was of no consequence during a siege.
The last device that was used was a battering ram. These were used to attack the weakest point in the enemy's defenses: the gate. The ram could be mounted in a siege tower, or it could be mounted inside it's own covered, wheeled structure. The ram was swung by two teams of men.
These devices helped prove the point that it was a bad idea to cross the Romans, and their mere existance forced many cities into surrender.