A siege is a group of invaders trying to attack or invade a castle. Sieges could last days, weeks, and even months at a time. The invaders thought if the people in the castle would run out of food and water they would be forced out of the castle. When this would happen the enemies could attack the people.
Catapults were not always used in the middle ages. The military also uses catapults today. The catapult has been used for hundreds of years. People used catapults to throw stuff over castle walls. Catapults made the job easier and more convenient for the attackers. Catapults are used by putting heavy rocks or boulders in a the dish and release it by the rope.