Prusias ad Hypium

Prusias ad Hypium (Ancient Greek: Προῦσα πρὸς τῷ Ὑππίῳ ποταμῷ) was a city in ancient Bithynia, and afterwards in the late Roman province of Honorias. In the 4th century it became a bishopric that was a suffragan of Claudiopolis in Honoriade. Before its conquest by King Prusias I of Bithynia, it was named Cierus or Kieros (Ancient Greek: Κίερος) and belonged to the Heraclea Pontica. Photius writes that it was called Kieros, after the river which flows by it.