Cersobleptes (, Kersobleptēs, also found in the form Cersebleptes, Kersebleptēs), was son of Cotys I, king of the Odrysians in Thrace, on whose death in September 360 BC he inherited the throne. From the beginning of his reign, however, Cersobleptes was beset by problems. He inherited a conflict with the Athenians and with the rebel former royal treasurer Miltokythes from his father, and now there appeared two rivals for the throne, Berisades and Amadocus II. Despite the continued able service of Cersobleptes' brother-in-law, the Euboean adventurer Charidemus, Cersobleptes was forced to make peace with Athens and with his rivals, recognizing them as autonomous rulers of parts of Thrace by 357 BC. The area controlled by Cersobleptes was apparently to the east of the rivers Tonzos and Hebrus, with Amadocus II to his west, and Berisades even farther west, on the border with Macedon. Charidemus had taken on a prominent role in the contests and negotiations with Athens for the possession of the Thracian Chersonese, with Cersobleptes appearing throughout as a mere puppet of Charidemus. The peninsula seems to have been finally ceded to the Athenians in 357 BC, though they did not occupy it with their settlers until 353 BC; Isocrates is less certain about the earlier date. For some time after the cession of the Chersonese, Cersobleptes continued to court the favor of the Athenians, being perhaps restrained from aggression by the fear of the Athenian fleet based in the Hellespont. In 357–356 BC, Philip II of Macedon began to expand at expense of his eastern neighbors, taking advantage of a rebellion among the allies of Athens to seize Amphipolis and Crenides, which he renamed after himself "Philippi," as well as the gold mines of Mount Pangaeum. Some of this expansion was at the expense of Berisades, who died about the same time, and was succeeded by his sons, Cetriporis and his brothers. Cersobleptes and Charidemus conceived the idea of depriving the sons of Berisades of their inheritance, and of obtaining possession of all the former dominions of Cotys. With this objective in mind Charidemus gained from the Athenian people, through his party among the orators, a decree in his favor. In response to this outcome, Demosthenes delivered a speech (which still exists) through which he unsuccessfully tried to impeach the mover of the decree, Aristocrates. But before the scheme of Cersobleptes and Charidemus could succeed, Cetriporis provoked the