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A military machine once used to hurl stones, spears, and other projectiles. Catapults were used mainly in sieges of castles and walled cities to project heavy stones against the walls, towers, and defenders of fortified places.
Most ancient catapults made use of tension or torsion to hurl projectiles. Tension was produced by bending bows or wooden planks, and torsion was produced by twisting ropes or fibers. Some catapults used a very heavy weight, called a counterpoise or counterweight, to hurl the projectile. Heavy catapults could hurl a 60-pound (27-kg) stone or an 8-foot (2.4-meter) spear 500 yards (457 meters). The catapult consisted of a long wooden arm of which one end was shaped as a cup to hold the stone in place, while the other was attached by strong cords to two upright posts joined by a crossbar. The cords were twisted by winches until the arm was horizontal and it was then secured by the notch of a large iron catch. Once the missile had been positioned in the cup the arm was released by striking the catch with a mallet, and the torsion force of the cords propelled the arm upwards and launched the stone into flight.
One of the earliest records of the use of a catapult is to be found in Plutarch's account of the siege of Syracuse by the Romans between 214-212 BC.
The ancient Romans had several types, one of which was called an onager. The onager consisted of a vertical beam whose lower end was mounted between two thick horizontal ropes twisted together. To load the onager, a windlass pulled down the beam, further twisting the ropes, and a heavy stone was then placed on the end of the beam or in a leather pouch at the end of the beam. When the beam was released, the torsion produced by the ropes snapped the beam back to its original vertical position and then hurled the stone toward its target with great force.
Catapults were largely superseded by cannon in the 14th or 15th century, although a few heavy machines were used as siege weapons in the 16th century.
In modern naval aviation the term "catapult" is applied to a track-mounted device used to launch airplanes from ships.