The article presents an attempt to reconsider the origin of the «Periplus of the Erythraean Sea». In contrast to the commonly accepted opinion which regards the «Periplus» as a kind of trader’s guide-book it is proposed to treat this source as a commentary to a map, which was lost. The origin of the «Periplus» is to be searched not from the point of view of commercial activity of its unknown composer, but rather in terms of cartographical ideas of a person who composed it on the basis of sources rooted in various traditions of different epochs. The principles of the supposed map go back to the pre- and Early Hellenistic ideas applied to the Egyptian views of the map orientation and personal experience of his own and/or that of his informants. The places visited by the author of the «Periplus» or/and his informants (African coast, India, Ceylon), are described with up-to-date accuracy. This means that their location was given according to special measurements; those poorly known (West Arabia) or never visited (China, Black Sea region) were described according to the archaic, unverifi ed ideas.