Engineering is the application of scientific and mathematical principles to the design and/or manufacture of theoretical systems and physical objects. Prior to the mid-18th century, military engineers carried out all engineering functions. Their work involved the construction of roads, bridges, fortifications, and the performance of other duties relating to the military. In the late 18th century, civil engineers took over all non-military engineering functions. Other fields of engineering prior to the 20th century included mining engineers, who designed mines and methods of mining, and mechanical engineers, who dealt with the design and construction of machinery. As new technologies developed, new fields of engineering developed along with them. Today, there are engineers specifically trained in nearly every field, from electronics and computers to chemistry and atomics.