(Κερσοβλέπτης), was son of Cotys, king of Thrace, on whose death in B. C. 358 he inherited the kingdom in conjunction with Berisades and Amadocus, who were probably his brothers. He was very young at the time, and the whole management of his affairs was assumed by the Euboean adventurer, Charidemus, who was connected by marriage with the royal family, and who bore the prominent part in the ensuing contests and negotiations with Athens for the possession of the Chersonesus, Cersobleptes appearing throughout as a mere cipher. (Dem. c. Aristocr. pp. 623, &c., 674, &c.) The peninsula seems to have been finally ceded to the Athenians in B. C. 357, though they did not occupy it with their settlers till 353 (Diod. 16.34); nor perhaps is the language of Isocrates (de Pac. p. 163d. μὴ γὰρ οἴεσθε μήτε Κερσοβλέπτην, κ. τ. λ.) so decisive against this early date as it may appear at first sight, and as Clinton (on B. C. 356) seems to think it. (Comp. Thirlwall's Greece, vol. v. pp. 229, 244.) For some time after the cession of the Chersonesus, Cersobleptes continued to court assiduously the favour of the Athenians, being perhaps restrained from aggression by the fear of their squadron in the Hellespont; but on the death of Berisades, before 352, he conceived, or rather Charidemus conceived for him, the design of excluding the children of the deceased prince from their inheritance, and obtaining possession of all the dominions of Cotys; and it was with a view to the furtherance of this object that Charidemus obtained from the Athenian people, through his party among the orators, the singular decree in his favour for which its mover Aristocrates was impeached, but unsuccessfully, in the speech of Demosthenes yet extant. (Dem. c. Aristocr. pp. 624, 625, 680.) [CHARIDEMUS.] From a passing allusion in this oration (p. 681), it appears that Cersobleptes had been negotiating with Philip for a combined attack on the Chersonesus, which however came to nothing in consequence of the refusal of Amadocus to allow Philip a passage through his territory. But after the passing of the decree above-mentioned, Philip became the enemy of Cersobleptes, and in B. C. 352 made a successful expedition into Thrace, gained a firm ascendancy in the country, and brought away a son of Cersobleptes as a hostage. (Dem. Olynth. i. p. 12 ad fin.; Isocr. Phil. p. 86c.; Aesch. de Fals. Leg. p. 38.) At the time of the peace between Athens and Philip in B. C. 346, we find Cersobleptes again involved in hostilities with the Macedonian king, who in fact was absent in Thrace when the second Athenian embassy arrived at Pella, and did not return to give them audience till he had completely conquered Cersobleptes. (Dem. de Fals. Leg. pp. 390, 391, de Cor. p. 235; Aesch. de Fals. Leg. pp. 29, 40, &c.) In the course of the next three years, Cersobleptes seems to have recovered strength sufficient to throw off the yoke, and, according to Diodorus, persisted in his attacks on the Greek cities on the Hellespont. Accordingly, in B. C. 343, Philip again marched against him, defeated him in several battles, and reduced him to the condition of a tributary. (Diod. 16.71; Ep. Phil. ad Ath. ap. Dem. pp. 160, 161; Dem. de Chers. p. 105.)