The Benin Moat (Edo: Iyanuwo), also known as the Benin City Iya, the Inner City Iya of Benin or the Wall of Benin, is a large earthwork within Benin City in Nigeria's Edo state, which formerly encircled the city at the time of the Benin Empire. It is the central part of a series of connected earthworks surrounding the city which are collectively known as the 'Benin City Walls', consisting of the massive Inner City earthwork and much smaller, though more extensive Outer City earthworks. Other earthworks are spread out across Edo State (known as the rural iya), and all of these earthworks are sometimes referred to collectively as 'the Walls of Benin'. All of these earthworks are known as Iya in the Edo language. With the exception of a small part of the Benin City Iya, these structures are not really 'walls' but rather linear earthworks, consisting of a ditch and earth rampart known as a 'dump rampart'. The Inner City Iya was built on a significantly larger scale with much taller ramparts and deeper ditches than any of the surrounding earthworks or other earthworks spread across the country, many of which are described as having a 'slight' and 'casual' profile. Most of these earthworks only served to delineate boundaries, whereas the Inner City Iya served a defensive purpose. Historical European accounts of the 'Benin Moat' or 'Benin City Wall' probably only refer to the Inner City Iya, though the accounts sometimes differ in their description of its structure. Several wooden entrance gates are said to have existed, but 19th century accounts make no mention of them and their remains have yet to be identified by archeological research. The Inner City Iya had a total length of approximately 12 kilometres (7.45 miles), though much of it has disappeared due to urban expansion and destruction in the modern era. The combined length of all of the earthworks across the entire country, including ditches and ramparts and boundary traces, has been estimated to be approximately 16,000 kilometres (9,900 mi), covering about 6,500 square kilometres (2,500 sq mi) of land, though little remains today. Whilst some sources have erroneously referred to these earthworks as comprising a single built structure, they actually consist of many different structures created at different times, some of which are connected and others which are not. These earthworks have deep historical roots, with evidence suggesting their existence before the establishment of the Oba monarchy. Construction may have begun as early as 800 AD, continuing up to the modern era. The Inner City Iya itself was built in c. 1460 AD. Its construction involved large-scale manual labour and the repurposing of earth from the outer ditch to build the inner rampart. It is estimated that a labour force of 5,000 men, working 10 hours a day, could have completed the work in 97 days, within the period of a single dry season.
Today, remnants of the Iya can still be found in Benin City, although urbanisation and land disputes pose challenges to their preservation. Recognised for their historical significance, the Benin Iya have been placed on a tentative list of Nigerian World Heritage Sites, though they have yet to be included in the official list by UNESCO. The Guinness Book of World Records describes 'The Linear Earthworks of Benin and Isha' as "the longest earthworks of the pre-mechanical era", though this refers to the estimated length of all the earthworks and boundary traces across the country combined and not specifically to the moat and rampart surrounding Benin City.
