A siege engine is a device that is designed to break or circumvent city walls and other fortifications in siege warfare. Some have been operated close to the fortifications, while others have been used to attack from a distance. From antiquity, siege engines were constructed largely of wood and tended to use mechanical advantage to fling stones and similar missiles. With the development of gunpowder and improved metallurgical techniques, siege engines became artillery. Collectively, siege engines or artillery together with the necessary troops and transport vehicles to conduct a siege are referred to as a siege-train.
