Initially raised at the court of Amadocus, Seuthes was sent to eastern Thrace several years before 405. By 405 he had managed to consolidate his position over a realm stretching from Apollonia Pontica over the Strandzha to parts of the northern Propontis coast. In 400 BC he hired Greek mercenaries under Xenophon to expand his dominion at the cost of Teres and other rebels, forcing them to reaknowledge the authority of Amadocus. Due to lacking funds they left his service already after two months. Seuthes II eventually rose against Amadocus, although little is known about this insurrection. In 389 the Athenian general Thrasybulus mediated between the two parties, resulting in Seuthes II, whom Xenophon called "ruler of the coast region", recognizing Amadocus' authority again.