From time to time one encounters a situation where a wisp of a source yields evidence of momentous consequence for the understanding of a whole society in the past. Such a situation raises the question of how much evidentiary weight a slender source can credibly bear, for when the evidence is so slender or tenuous, the slightest misunderstanding or misinterpretation can lead to hugely magnified errors in historical reconstruction. At the same time, the more slender the evidence, the more tempted researchers will be to interpret it according to their own a priori vision of the past in question. This is a genuine problem which can only be overcome by finding more relevant evidence.
Such situations naturally crop up wherever sources (written or otherwise) are very rare, so that every scrap of evidence must be scrutinized and exploited with the greatest care and to its fullest extent, a common circumstance in African history in relation to written documents before ca. A.D. 1450 and documents at all times about topics such as, for instance, women's history or specific techniques of agriculture that were normally not recorded. The situation then, while unusual, is frequent enough to warrant a more detailed discussion of one such instance to illustrate what the problem is and how it can be tackled. This illustration will be the case of oratoi, a single word in the Periplus Maris Erythraei.
The Periplus is justly famous in African historiography. Known from a single manuscript now in Heidelberg and held to date from the early tenth century and a much later copy from that now in the British Museum, written in a mixture of classical and vulgar Greek by either a Greek living in Egypt or an Egyptian, and firmly dated to between AD 40-55, the Periplus contains the first, albeit succinct, information about the inhabitants of the East African coast, more than half a millennium before other comparable written mentions occur.