Sestos is a town in Thrace, situated at the narrowest part of the Hellespont, opposite Abydos in Asia, from which it was only seven stadia distant. It was founded by the Aeolians (Herod.vii. 33). It was celebrated in Grecian poetry on account of the loves of Leander and Hero (see Leander), and in history on account of the bridge of boats which Xerxes here built across the Hellespont. It was taken by the Romans in B.C. 190.
(from Harpers Dictionary of Classical Antiquities, 1898)
Abydos is a town of the Troad on the Hellespont, and a Milesian colony, nearly opposite to Sestos, but a little lower down the stream. The bridge of boats which Xerxes (q.v.) constructed over the Hellespont, B.C. 480, commenced a little higher up than Abydos, and touched the European shore between Sestos and Madytus.