Sungbo's Eredo, as it is called, is really an earthen embankment with an accompanying ditch. Whatever you call it, it does enclose an area 25 miles north-to-south and 22 miles east-to-west. That's a lot of earth-moving, for at some spots the "wall" measures 70 feet from the bottom of the ditch to the top of the embankment. Today, this impressive structure is mostly concealed by the Nigerian jungle. A thousand years ago it enclosed a flourishing African kingdom.