Europa was a Roman province within the Diocese of Thrace. Established by Roman Emperor Diocletian in 314, the province's capital was Perinthus. The province largely corresponds to what is modern day European Turkey. Bordering only the provinces of Rhodope and Haemimontus to the west and northwest, Europa was a peninsula and was surrounded by water on three sides: the Black Sea to the northeast, the Bosphorus to the east, and the Sea of Marmara and Aegean Sea to the south and southeast. The largest city along the Black Sea was Salmydessus. Along the coast of the Sea of Marmara were the cities of Perinthus (later known as Heraclea), Selymbria, Raidestus, and Callipolis. On the coast of the Aegean and at the mouth of the Hebrus river in the Melas Gulf was the city of Aenus (Thrace).