Wikipedia: Medieval siege weaponry

Medieval siege weaponry was in the beginning very similar to the weaponry used in Roman times. Among the weapons used were the ballista?, the siege tower, the [battering ram]? and the famed catapult. Later, technological advances in wall construction lead to development of the trebuchet?. The principal raison d'etre of siege weaponry was, of course, siege warfare, usually of heavily fortified and well prepared defensive positions such as the castle? or [city wall]?s.

With the advent of gunpowder and the consequent development of firearms such as the arquebus? and the cannon in the latter part of the middle ages a process was set in motion which would inexorably result in a virtual abandonment of the encastellated fortification as a means of defense.