There are two major island groups known as Prince's and Marmara islands. The latter group is rich in sources of marble and gives the sea its name (marmaros is the Greek word for marble).
Propontis (Προποντίς, -ίδος) was the ancient Greek name for the sea. The name derives from pro (before) and pont- (sea): the Greeks commonly sailed through the Propontis to reach the Black Sea.
Land is bordered by the three seas being, Pontus Euxinus (Black Sea) on north, by Aigaios Pelagos (Aegean Sea) on west, by Thalassa (Mediterranean Sea) on south and an inner sea Propontis (sea of Marmara) on the northwest.
The Seas of Pontus Euxinus and Propontis are connected with a long narrow strait known as Bosporus Thrakios (Bosphorus).
Propontis sea is separated from Aigaois Pelagos by another strait Hellespont or Dardanelles.
It was bounded by Lydia and Phrygia on the south, by Bithynia on the north-east, and by the Propontis and Aegean Sea on the north and west.
In the northern portion of the province are two considerable lakes, Artynia[?] or Apolloniatis (Abulliont Geul), and Aphnitis[?] (Maniyas Geul), which discharge their waters into the Macestus from the east and west respectively.
The most important cities were Pergamum in the valley of the Caicus, and Cyzicus on the Propontis.