Benin City's moats and ramparts stretched some 16,000 kilometres
The walls of Benin, in present-day Nigeria, combined ditches and earth ramparts across more than 500 linked settlement boundaries. Journalist Fred Pearce put their length at four times that of the Great Wall of China, built with a hundred times the material of the Great Pyramid.
A moat is a broad, deep ditch, wet or dry, circling a castle or town to hold off attackers, especially siege engines. By blocking land access except at a few bridges or causeways, it funnels assaults into points easier to defend. Siege towers and battering rams had to reach the wall to work, and water made tunnelling under the defences extremely difficult. Builders named variants: neck ditches cut across a spur, cross ditches divided inner and outer wards, and segmented moats mixed wet and dry stretches.
Some of the earliest evidence comes from Egyptian fortresses such as Buhen in Nubia, as well as from Babylon and Assyrian reliefs. The English word traces to the Old French motte, a mound, first used for the castle mound itself before shifting to the ring dug around it. When siege artillery arrived, 16th-century bastion fortresses known as the trace italienne still relied on moats, and they persisted around the polygonal forts of the mid-19th century.
In Benin City, the Edo people dug an inner ditch and heaped the spoil into an outer rampart, a system called Iya, with construction thought to have run from about 800 to the mid-15th century. The walls enclosed 6,500 square kilometres and took an estimated 150 million hours of digging. British forces ravaged them in 1897, and surviving sections are still being cleared for development.
Japanese castles could have up to three concentric moats. Feudal ones were often dry trenches, including tatebori dug down slopes, while water moats are more common today; the Tokyo Imperial Palace moats now host rental boats, fishing ponds and restaurants. Moats also surround Angkor Wat, Beijing's Forbidden City and Mandalay. The Mississippian culture of North America developed them independently, and Australia's only moated fort, Fort Lytton in Brisbane, was built in 1880 and 1881 amid fears of a Russian invasion.
Source: Moat
