As the Middle Ages progressed new technologies came into battle. In terms of warfare, there was the trebuchet, the famous catapult, and siege towers.
Siege towers were used to clear a castle wall and invade the town below. Siege towers were a simple but highly effective strategy. Basically the invaders would build a small armored tower, add wheels to it and then push it against the enemy wall. Some times there would be a platform lowered so people could walk into the town below. A problem with siege towers was that it took time to construct. In response to a siege tower the defenders would shower down flaming arrows in an attempt to turn the tower into a fiery inferno. To defend against fire, iron plates were attached to the tower's sides, although this was rarely done because it was too difficult. Siege towers were fairly efficient and used often.