Contemporary studies in historical geography have not yet elaborated any convincing idea of the origin of the notion of the «Red Sea». In general, they follow the efforts of the Classical thought to find this origin in the «redness» of the natural colour of surrounding water or sand. From the other side it is supposed that the «Southern» sea in Iranian tradition must have been seen as «red» (while the «Northern» one as black) and this was spread throughout the ancient world. However, neither the blackness of the Northern sea nor the redness of the Southern sea can be supported by ancient sources. In the geographical scheme of Herodotus the Red Sea is represented in the west, south and east of the Oikumene. A good deal of relevant information can be found in cosmogonical myths of ancient Greek, Scandinavian, Indian and Iranian traditions. With some variations they report the struggle between a «hero» (Kronos in ancient Greece, Odin and other gods in Scandinavia, Indra – in ancient India and Traitaona in ancient Iranian tradition) and his opponent (Uranos in ancient Greece, Imir in Scandinavia, Vr$tra in India and Dahaka in ancient Iran), whose blood is flowing into the «waters», i.e. into the «Outer Sea». In the Iranian tradition farn – the royal celestial shining – falls into the Surrounding sea, which thus becomes red. The notion of the «Red sea» reflects the most ancient Indo-European cosmogonic ideas of the «Outer Sea» and has no connection with any opposition of the parts of the World Ocean and its colours. The origin of the name «Black sea» must also be searched for elsewhere.