I felt my heart thumping and heard my breathing grow louder and it took a second or two before I realised that it was carbon-dioxide that I was gasping and made for the ladder. Together with Robert Soper, I had been measuring the belled-out base of an ancient, empty water cistern in Old Oyo when this incident occurred; and that measurement was never completed.

This was just one of numerous archaeological features at Old Oyo - grinding stones, ash mounds, exquisitely decorated pottery, old wells, a reservoir, a complex of ancient wall mounds, and numerous old compound walls and banks. During rainy season surveys there, the sword grass sliced through my jeans; and during the dry season the sweat bees were incessant, especially near the water holes.

Many years later, I returned with forest guards; and camping out under the stars, I heard the last lioness roar in the dark as she went down to drink 400 yards away. The breeze in the borassus palms sounded like the restless spirits of the Oyo ghosts. So many of its kings had been forced to commit suicide here; and three virgins were sacrificed at different stages along the route to Bara - the royal burial grounds to the north.

This lay alongside Kosso, where an early Oyo king, Shango, hanged himself. Its ancient mud-coursed walls still rise six metres high in some places; and its walls link up with those of Old Oyo. Shango became deified as the God of Thunder; and his fiercesome cult still exacts the ultimate penalty among those whose ancestors migrated to the New World. Kosso was very probably Oko Oyo, the original Oyo city, which would explain the location of Bara here.