THE WALLS OF BENIN CITY
The Walls of Benin, located in Benin City Edo State, were used as a defence of the defunct Kingdom of Benin, which is now Benin City, the capital of Edo state. It is considered the largest man-made structure lengthwise and hailed as the largest earthwork in the world.
The construction was estimated to have started in 800 and continued into the mid-15th century. It is considered one of the greatest achievements of man in the 13th century, considering that there was no use of machines.