（*Prousi/as), king of Bithynia, was the son of Zielas, whom he succeeded on the throne, and grandson of NICOMEDES I.
The date of his accession is unknown, but it appears that it preceded the death of Antiochus Hierax, and may therefore be placed at least as early as B. C. 228, (Trog. Pomp. Prol. xxvii.; Clinton, F. H. vol. iii. pp. 413, 414; Niebuhr, Kl. Schrift. p. 287.)
The first event of his reign, which is recorded to us, is a war with the Byzantines, in which we find him engaging in B. C. 220, in conjunction with the Rhodians.
The latter were at first supported by Attalus, king of Pergamus, as well as by Achaeus, who had lately assumed the sovereignty of Asia Minor, and they endeavoured also to set up Tiboetes, the uncle of Prusias, as a competitor for the throne of Bithynia. Their efforts were, however, unsuccessful: Prusias conquered all the possessions of the Byzantines in Asia, while the Thracians pressed them closely on the European side, and they were soon comp