This paper describes a large area of stone-built ruins in northern Tanzania which has so far only been briefly excavated, but which is likely to prove to be a key site in the study of the Iron Age in East Africa. In addition to numerous massive stone circles, terraces and cairns, there are extensive systems of fields and enclosures defined with lines of stones. Excavations carried out in 1964 and 1966 have shown that the small terrace-platforms on the hillsides and the stone circles on the flatter land in the valley were occupied at different periods and by different peoples whose pottery is readily distinguishable. Radiocarbon dates suggest that the terrace sites on the hillsides were occupied during the first millennium A.D., and that the stone circles on the lower slopes in the valley were occupied during the fifteenth century A.D. The purpose of the numerous large and well-built cairns is not yet known, but it appears that they were not burial monuments. No evidence has been found that any of the stone structures were built or occupied by immigrants from outside Africa.

It has not yet been possible to link the systems of fields and enclosures to the hillside terrace-platforms or to the stone circles. A close examination of the main area of fields and of low-level aerial photographs has not produced any evidence that the fields were irrigated, a fact which raises important agricultural and climatic problems in an area which has an average rainfall of less than 380 mm. (15 inches).

The general picture of Engaruka which emerges is of an area which was occupied by different peoples at different times over a period of at least a thousand years. The stone structures which these different peoples built have accumulated to give the impression that there was once a very large population living in the area; in fact it is possible that this population was always less than 4,000 people at any one time.