High Quality Content by WIKIPEDIA articles! The Walls of Benin was a combination of ramparts and moats called Iya that was used as a defense of the capital Benin City, in present day Edo State of Nigeria. IT was considered the largest man-made structure lengthwise, second only to the Great Wall of China and the largest earthwork in the world. WIth more recent work by Patrick Darling, it has been established as the largest man-made structure in the world, larger than Sungbo's Eredo. IT enclosed 6,500 km² of community lands. ITs length was over 16,000 km of earth boundaries. IT was estimated to have been built starting earliest from 800 AD continuing into the mid 1400's.