A trip hammer (alt. helve hammer) is a massive power hammer, usually raise by a cam and then released to fall under the force of gravity. Historically, trip hammers were often powered by a water wheel, known to be used in China as long ago as the Han Dynasty (202 BC–220 AD), and in medieval Europe by the 12th century. During the Industrial Revolution multiple hammers were powered via a set of line shafts, pulleys and belts from a centrally located power supply.