Helenopolis (Greek: Ἑλενόπολις) or Drepana (Δρέπανα) or Drepanon (Δρέπανον) was an ancient Thracian and later Greco-Roman and Byzantine town in Bithynia, Asia Minor, on the southern side of the Gulf of Astacus.
Helenopolis has been identified with the modern village of Hersek, in the district of Altınova, Yalova Province.
Nearby, in the late 11th century, Alexios I Komnenos built a castle called Kibatos or Civetot for Anglo-Saxon mercenaries who had opted to flee England after the Norman Conquest and serve the Byzantine Emperor.
The remains of the castle span approximately 4,200 square meters and were identified based on architectural similarities to contemporary descriptions.
[2] In addition to the discovery of the castle - believed to have been abandoned due to earthquakes at an indeterminate time - among other structures, remains of a pier and lighthouse were found, which were visited by Evliya Çelebi and are known to have been used from the Byzantine period right up until the demise of the Ottoman Empire.
About 400, the church of Helenopolis was governed by Palladius of Galatia, the friend and defender of John Chrysostom, and author of the Historia Lausiaca.