Catapult, a device that throws objects through the air. In ancient and medieval times, the catapult was a military weapon. It was used to hurl large rocks, wooden beams, arrows, lances, and flaming casks of Greek fire.

Catapults appeared in many shapes and sizes. The ballista worked somewhat like a crossbow. The onager consisted of a huge arm that was held in a horizontal position while under the tension of elastic animal fibers. When the tension was released suddenly, the arm flew forward and upward, hurling the missile. The trebuchet was similar to the onager but used weights to supply the tension.

The catapult is believed to have been invented by Dionysius of Syracuse in 399 B.C. The development of cannon in the 14th century made the weapon obsolete. A modern form of catapult, operated by steam, is used to launch jet airplanes from an aircraft carrier.