Cyzicus ( SIZ-ik-əs; Ancient Greek: Κύζικος, romanized: Kúzikos; 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 (the classical Arctonnesus), 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.
The site of Cyzicus, located on the Erdek and Bandırma roads, is protected by Turkey's Ministry of Culture.
The city was said to have been founded by Pelasgians from Thessaly, according to tradition at the coming of the Argonauts; later it received many colonies from Miletus, allegedly in 756 BC, but its importance began near the end of the Peloponnesian War when the conflict centered on the sea routes connecting Greece to the Black Sea. At this time, the cities of Athens and Miletus diminished in importance while Cyzicus began to prosper. Commander of the Athenian fleet Alcibiades defeated the Spartan fleet in a major naval engagement near Cyzicus known as the Battle of Cyzicus in 410 BC. Famed ancient philosopher Eudoxus of Cnidus established a school at Cyzicus and went with his pupils to Athens, visiting Plato. Later he returned to Anatolia to his hometown of Cnidus, and died circa 350 BC. The era of Olympiads in Cyzicus was reckoned from 135 or 139.
Owing to its advantageous position it speedily acquired commercial importance, and the gold staters of Cyzicus were a staple currency in the ancient world till they were superseded by those of Philip of Macedon. Its unique and characteristic coin, the cyzicenus, was worth 28 drachmae.
During the Peloponnesian War (431–404 BC) Cyzicus was subject to the Athenians and Lacedaemonians alternately. In the naval Battle of Cyzicus in 410 during the Peloponnesian War, an Athenian fleet routed and completely destroyed a Spartan fleet. At the peace of Antalcidas (387 BC), like the other Greek cities in Asia, it was made over to Persia. Alexander the Great later captured it from the Persians in 334 BC and was later claimed to be responsible for connecting the island to the mainland.
The history of the town in Hellenistic times is closely connected with that of the Attalids of Pergamon, with whose extinction it came into direct relations with Rome. Cyzicus was held for the Romans against King Mithridates VI of Pontus who besieged it with 300,000 men in 74 BC, the Siege of Cyzicus, but it withstood him stoutly, and the siege was raised by Lucullus: the loyalty of the city was rewarded by an extension of territory and other privileges. The Romans favored it and recognized its municipal independence. Cyzicus was the leading city of Northern Mysia as far as Troas.
Under Tiberius, it was incorporated into the Roman Empire but remained the capital of Mysia (afterwards, Hellespontus) and became one of the great cities of the ancient world.
There was a women's cult at Cyzicus worshiping the goddess Artemis, which was called Dolon (Δόλων).
Cyzicus was captured temporarily by the Arabs led by Muawiyah I in AD 675. It appears to have been ruined by a series of earthquakes beginning in 443, with the last in 1063. Although its population was transferred to Artake before the 13th century when the peninsula was occupied by the Crusaders, in 1324 the metropolitan of Cyzicus was one of three sees in Anatolia which was able to contribute a temporary annual subsidy to the Patriarchate of Constantinople. Following its conquest by the Ottomans it underwent hard times. From a point between 1370 and 1372 until 1387, the metropolitan was empty; Speros Vryonis speculates this was due to financial difficulties. Later in the 14th century, the sees of Chalcedon and certain patriarchal possessions in Bithynia and Hellespont were bestowed on the metropolitan of Cyzicus.
In the Ottoman era, it was part of the kaza of Erdek in the province of Brusa.
Cyzicus, as capital of the Roman province of Hellespontus, was its ecclesiastical metropolitan see. In the Notitiae Episcopatuum of Pseudo-Epiphanius, composed in about 640, Cyzicus had 12 suffragan sees; Abydus, Baris in Hellesponto (between Sariköy and Biga), Dardanus, Germa in Hellesponto (ruins of Germaslu, Kirmasti, Girmas), Hadrianotherae (Uzuncia yayla), Ilium, Lampsacus, Miletopolis, Oca, Pionia (Avcılar), Poemanenum (Eskimanias), Troas. The province also included two autocephalous archiepiscopal sees: Parium and Proconnesus.
After the Ottoman conquest of the region, Cyzicus faced such major decline, that in 1347 it received the diocese of Ganos, as to better cover its own expenses. In 1370 and in 1372 the seat remained without a Metropolitan until 1381. In 1387, when a new Metropolitan assumed the see, he received the diocese of Chalcedon, along with its treasury in Constantinople. Cyzicus also received some additional possessions of the Patriarchate in Bithynia and the Hellespont, as to keep the metropolitanate functioning.
Cyzicus had a catalogue of bishops beginning with the 1st century; Michel Le Quien mentions fifty-nine. A more complete list is found in Nicodemos, in the Greek "Office of St. Emilian" (Constantinople, 1876), 34–36, which has eighty-five names. Of particular importance are the famous Arian theologian Eunomius of Cyzicus; Saint Dalmatius; Caesar Basiliscus; bishops Proclus and Germanus, who became Patriarchs of Constantinople; and Saint Emilian, a martyr in the 8th century. Another saint who came from Cyzicus, Saint Tryphaena of Cyzicus, is the patron saint of the city. Gelasius, a historian of Arianism, who wrote about 475, was born at Cyzicus.
Diogenes, Metropolitan of Cyzicus before 449 and after 451
Constantine Stilbes, Metropolitan of Cyzicus in ca. 1204
George Kleidas, Metropolitan of Cyzicus in ca. 1253–61
Theodore Skoutariotes, Metropolitan of Cyzicus in ca. 1277
Daniel Glykys, Metropolitan of Cyzicus in 1285–89