Ancient Rome had eleven major aqueducts, built between 312 B.C. The longest aqueduct was 59 miles long. Water was instead usually supplied through the digging of wells, though this could cause serious public health problems when local water supplies became contaminated. One notable exception was the New River, a man-made waterway in England, opened in 1613 to supply London with fresh drinking water over a distance of 38 miles (62 km). The development of canals provided another spur to aqueduct building. However, it was not until the 19th century that aqueduct building resumed on a large scale to supply fast-growing cities and water-hungry industries. The developments of new materials (such as cast iron) and new technologies (such as steam power) enabled significant improvements to be made. Aqueducts were used to supply water for the city. People needed water to drink and to work.