Cyzicus was an ancient Greek town in Mysia in Anatolia in the current Balıkesir Province of Turkey. It was located on the shoreward side of the present Kapıdağ Peninsula, a tombolo which is said to have originally been an island in the Sea of Marmara only to be connected to the mainland in historic times either by artificial means or an earthquake.

Mysia was a region in the northwest of ancient Asia Minor. It was located on the south coast of the Sea of Marmara. It was bounded by Bithynia on the east, Phrygia on the southeast, Lydia on the south, Aeolis on the southwest, Troad on the west, and the Propontis on the north. In ancient times it was inhabited by the Mysians, Phrygians, Aeolian Greeks and other groups.