Helenopolis or Drepana was an ancient Roman and Byzantine town in Bithynia, Asia Minor, on the southern side of the Gulf of Astacus. It has been identified with the modern village of Hersek, in the district of Altınova, Yalova Province. It is traditionally considered as the birthplace of St. Helena.
According to the 6th-century historian Procopius, Helena's son Constantine the Great renamed the city "Helenopolis" to honor her birthplace; but the name may simply have honored her without marking her birthplace. Constantine also built there a church in honour of the martyr St. Lucian; it soon grew in importance, and Constantine lived there very often towards the end of his life.
Justinian built there an aqueduct, baths, and other monuments. It does not seem ever to have grown, and it was slightingly called Eleinou Polis, "the wretched town".
Ecclesiastical history 
Helenopolis was suffragan of Prusa.
Lequien mentions nine of its bishops. Macrinus, the first, is said to have been at the Council of Nicaea (325), but his name is not given in the authentic lists of the members of the council. 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. The last known bishop assisted at the Photian Council in Constantinople (879). Helenopolis occurs in the Notitiae Episcopatuum until the twelfth and thirteenth centuries.
Helenopolis is a Catholic titular see (Italian Elenopoli di Bitinia).
- Harbus, Antonia. Helena of Britain in Medieval Legend. Rochester, NY: D.S. Brewer, 2002, p. 12ff
- Oriens Christianus, I, 623.