🇳🇬 Nigeria · Earthwork
Benin City Walls (Iya)
Early to Late Edo Kingdom (800–1897 CE; peak 13th–16th c) · Edo (Bini) / Igodomigodo → Kingdom of Benin
16,000 km of ramparts and 20 m high ditch-bank earthworks enclosing 6,500 km² – world's longest pre-mechanical earthwork.