A laborer is a skilled trade, a person who works in manual labor types, especially in the construction and factory industries. Laborers are in a working class of wage-earners in which their only possession of significant material value is their labor. Industries employing laborers include building things such as roads, road paving, buildings, bridges, tunnels, pipelines civil and industrial, and railway tracks. Laborers work with blasting tools, hand tools, power tools, air tools, and small heavy equipment, and act as assistants to other trades as well such as operators or cement masons. The 1st century BC engineer Vitruvius writes that a good crew of laborers is just as valuable as any other aspect of construction. Other than the addition of pneumatics, laborer practices have changed little. With the introduction of field technologies, the laborers have been quick to adapt to the use of this technology as being laborers' workforce.