The article outlines the range of problems relevant for the modern study of Hellenistic history. It analyses some rather obscure accounts of ancient sources on the war between the coalition of Rhodes and Bithyne against Byzantion. This conflict is often considered as a «trade war». The hostilities broke out because of the tax policy started by Byzantion as an answer to the pressure of the Celtic kingdom of Tylis. Before that Rhodes policy was based on neutrality and non-interference. A critical revision of the scanty evidence of written sources in correlation with epigraphic, numismatic and archaeological data, allows the author to undertake a detailed reconstruction of the course of the war. The events around Sinope and the war in Crete (in which Rhodes participated more or less actively) are to be dated to the same time or a little later than the hostilities at Thracian Bosporus. In these three events Rhodes demonstrated new features which were to become characteristic of its policy later on: its care for the security of sea trade and its struggle against the pirates.