Pit Structures are estimated to number into many hundreds. They are found singly, or more rarely, grouped in pairs in a single platform, or in groups of up to twelve or more. The following features characterize all pit structures: they are almost always on sloping ground and they form the centre of an artificial platform, about 20 metres across, which is retained by a stone wall on the lower slopes of the hill.
Every visitor will have heard of Nyanga’s “slave pits" but no evidence has ever been produced to support the theory that they were occupied by slaves who cultivated the nyanga terraces, and the term "pit structures" is now used. Other interpretations for the pits have included fortified refuges for women and children in case of attack; prisons for slaves being transported by Arabs to the coast; grain stores; gold washing tanks; cattle, goat or sheep kraals. A visit to this reconstructed pit structure should help visitors come to a decision on their historic function.
The pits themselves are beautifully made of close fitting stones laid without mortar and are generally about 5 to 10 metres wide and 3 metres deep. No traces of roofing have ever been found, either round the tops of the pits, or as fallen fragments, within them. They must always have been open and this indicates that they could not have been intended for people to live in, which rules out their use by slaves.
The floors of the pits were paved in stone, sloping down to a large stone lined drain, which ran under the platform and away. Frequently, large ditches lead from the drain to small earthwork dams, or to the tunnel of a second pit, lower down the hill slope, and so through this pit and drain and away. This is evidence of a regular flow of water flushing the pits; and would seem to rule out any possibility of the pits being used for the storage of grain which would need, above all, protection from damp.