Old Oyo is the site of a large city deserted in about 1837 A.D. The old palace compound and a past water reservoir lie within the 200 ha area enclosed by a 7.5 km long wall. Two concentric outer walls with ditches, l 8 and 28 km long, enclose nearly 3,000 ha: one third of this is covered by the ruins of past mud buildings and one third by sherd scatters presumed to have occurred under more ephemeral housing. Guard houses in the wall gateways, wells, cisterns and grinding hollows provide parallel evidence of a very extensive past settlement. The mud-block construction of the old walls is best exemplified on a 16 km long wall loop, which encloses a further 2.000 ha.