Heavy equipment refers to heavy-duty vehicles, specially designed for executing construction tasks, most frequently, ones involving earthwork operations. They are also known as, construction equipment, construction plant, earth movers, engineering vehicles, or just plain equipment. They usually comprise five equipment systems: implement, traction, structure, power train, control and information. Heavy equipment functions through the mechanical advantage of a simple machine, the ratio between input force applied and force exerted is multiplied. Currently most equipment use hydraulics as a primary source of transferring power. The use of heavy equipment has a long history; the ancient Roman engineer Vitruvius (1st century BCE) gave detailed descriptions of heavy equipment and cranes in ancient Rome in his treatise De architectura.