(anc. geog.), metropolis of Bithynia, built by Nicomedes the grandfather of Prusias. Situated on a point of the Sinus Astacenus, (Pliny); furred the Beautiful, (Atheneus); the largest city of Bithynia, (Pausanias), who says it was formerly called Aflacus; though Pliny distinguishes Astacum and Nicomedia as different cities. Nicomedia was very famous, not only under its own kings, but under the Romans; it was the royal residence of Diocletian, and of Constantine while Constantinople was building, if we may credit Nicephorus. It is still called Nicomedia, at the bottom of a bay of the Propontis in the Hither Asia. E. Long. 30° 0'. N. Lat. 41° 20'.