Dia (), also Diospolis (Διόσπολις), was a port city of
ancient Bithynia
Bithynia (; ) was an ancient region, kingdom and Roman province in the northwest of Asia Minor (present-day Turkey), adjoining the Sea of Marmara, the Bosporus, and the Black Sea. It bordered Mysia to the southwest, Paphlagonia to the northeast a ...
on the
Pontus Euxinus
The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bound ...
in
Asia Minor
Anatolia (), also known as Asia Minor, is a peninsula in West Asia that makes up the majority of the land area of Turkey. It is the westernmost protrusion of Asia and is geographically bounded by the Mediterranean Sea to the south, the Aegean ...
Ptolemy
Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
has. There are some very rare coins with the epigraph ''Dias'' (Διας), which Sestini assigns to this place.
Its site is located near
Akçakoca
Akçakoca is a town in Düzce Province, in the West Black Sea Region of Turkey, located about 200 km east of Istanbul. It is the seat of Akçakoca District.Asiatic Turkey.