Longest earthworks of the pre-mechanical era

The longest earthworks in the world carried out prior to the mechanical era are the Ancient Linear Earthworks of Benin and Ishan, located in Edo State in present-day Nigeria. In 1977 it was estimated by Dr Patrick Darling that the total length of the earthworks was probably 16,000 km (10,000 miles) with the total amount of earth moved estimated at 150 million m³ (200 million yd³). The earthworks were first reported in 1903 and partially surveyed in 1967. Radio carbon research indicates that they were built from about 700 AD to 1400 AD. The earthworks may have first been dug as steep ditches to keep elephants out of farmlands; but over time they served as agricultural boundaries and social boundaries (women could cross and marry out into nearby villages but the men stayed put); and they were also became perceived as providing protection from evil spirits.