A steamroller (or steam roller) is a form of road roller – a type of heavy construction machinery used for leveling surfaces, such as roads or airfields – that is powered by a steam engine. The leveling/flattening action is achieved through a combination of the size and weight of the vehicle and the rolls: the smooth wheels and the large cylinder or drum fitted in place of treaded road wheels. The word steamroller frequently refers to road rollers in general, regardless of the method of propulsion.