Castles were constructed of wood, stone and ... brick. A large number of contemporary accounts have survived that explain how castles were built. A large skilled workforce was needed to construct castles, including ditch diggers, stonecutters, masons, carpenters, and engineers. Medieval machines and inventions, such as the treadwheel crane, became indispensable during construction, and techniques of building wooden scaffolding were improved upon from Antiquity.[5] Nevertheless, castles could take many years to complete, although the time needed depended greatly from type, location, resources, time period, construction materials, etc.