A ballista is an ancient missile weapon that resembles a large crossbow. It was used primarily in warfare to launch projectiles, such as large bolts or stones, over long distances. The design allowed for greater accuracy and power compared to traditional catapults, making it effective in sieges and battles. Ballistae were typically made of wood and operated by a system of twisted ropes or springs to store energy. They were often used by ancient civilizations, including the Romans and Greeks, and played a significant role in military tactics during their time.