The Erythraean Sea (Ancient Greek: Ἐρυθρὰ Θάλασσα, Erythrà Thálassa, lit.

The area referred to by this name frequently extended beyond the Gulf of Aden—as in the famous 1st-century Periplus of the Erythraean Sea—to designate all of the present-day Red Sea, Arabian Sea, Persian Gulf, and Indian Ocean as a single maritime area.

The Greeks themselves derived the name from an eponymous King Erythras and knew that the waters so described were deep blue.

[2][3] Modern scholars sometimes attribute the name to the seasonal blooms of the red-hued Trichodesmium erythraeum in the Red Sea.

[4] Agatharchides had written of the origin of the name Erythraean Sea on the book (De Mari Erythraeo, § 5) in a story about the king Erythras: "There was a man famous for his valor and wealth, by name Erythras, a Persian by birth, son of Myozaeus.... the glory of the Island ascribed to him by the popular voice because of these his deeds, that even down to our own time they have called that sea, infinite in extent, Erythraean Sea".