PORTHMUS(Πόρθμος), a harbour in Euboea, belonging to Eretria, described by Demosthenes as opposite to Attica, is the modern Porto Búfalo, immediately opposite to Rhamnus, in the narrowest part of the Euboean channel, where the breadth is only two miles. It was destroyed by Philip, after expelling the Eretrians; but its advantageous position close to the coast of Attica gave it importance for many centuries afterwards. (Dem. Phil. iii. pp. 119, 125, 4. p. 133, de Cor. p. 248; Plin. Nat. 4.12. s. 21; Hierocl. p. 645; Harpocrat. Phot. Suid. s. u.Πόρθμος;Leake, Northern Greece, vol. 2. p. 435.)