Even before the conquest by Alexander, the Bithynians appear to have asserted their independence, and successfully maintain it under two native princes, Bas and Zipoites, the latter of whom assumes the title of king (basileus) in 297 BCE.

His son and successor, Nicomedes I, founds Nicomedia, which soon rises to great prosperity, and during his long reign (c. 278 – c. 255 BCE), as well as those of his successors, Prusias I, Prusias II and Nicomedes II (149 – 91 BCE), the kingdom of Bithynia holds a considerable place among the minor monarchies of Anatolia.

But the last king, Nicomedes IV, is unable to maintain himself against Mithridates VI of Pontus, and, after being restored to his throne by the Roman Senate, he bequeaths his kingdom by will to the Roman republic (74 BCE).

The coinage of these kings shows their regal portraits, which tend to be engraved in an extremely accomplished Hellenistic style.