This episode examines the trebuchet, a fearsome, gravity-powered catapult that flung stone missiles with great speed, accuracy and destructive power. The first large-scale mechanized weapon, it transformed medieval warfare. Two teams of timber framers, engineers and historians attempt to build replicas of this 13th-century deterrent. Armed only with traditional tools, the teams work in a swampy field beside Loch Ness in northern Scotland. As the giant wooden catapults stand poised to fling 250-pound stones into the air, NOVA recaptures the suspense, violence and ingenuity that characterized the medieval siege.

Tuesday, 1/24 from 8-9 p.m. ET