A GIS Approach to Finding the Metropolis of Rhapta

The Periplus of the Erythrean Sea is a description of trade networks in the western Indian Ocean written as a guide for merchants (Casson 1989: 5). This text provides a description, varying in detail, of a multitude of regions, including the geographic features, settlements, ports, and peoples to be found in each. The original text, dating to approximately 30–40 CE, no longer survives, but a copy, believed to date to the tenth century, has been preserved and is currently housed in Heidelberg (Graf 1994: 143). The southernmost location mentioned in the text is the port of Rhapta, on the East African coast. This port is also mentioned in Ptolemy’s Geography, a second-century CE geographical account, in which it is termed a mētropolis and located “a short distance from the sea” (mikron apothen thalassēs), that is, the mouth of the Rhaptos river which flowed into the Indian Ocean (4.7.12). The exact location of Rhapta has been the subject of a lengthy historical debate owing to a lack in the text of any description of recognizable geographic features associated with, and the absence of any notable archaeological sites that can unequivocally be attributed to, the port (Hoyle 1967: 95; Horton 1990: 97; Kirwan 1986: 99).