The place is said to have been colonized by Bottiaeans, and to have originally borne the name of Ancore (Ἀγκόρη) or Helicore (Ἑλικόρη), or by soldiers of Alexander the Great's army who hailed from Nicaea in Locris, near Thermopylae.

[12] Whatever the truth, the first Greek colony on the site was probably destroyed by the Mysians, and it fell to Antigonus I Monophthalmus, one of Alexander's successors (Diadochi) to refound the city c. 315 BC as Antigoneia (Ἀντιγονεία) after himself.

described the city as built in the typical Hellenistic fashion with great regularity, in the form of a square, measuring 16 stadia in circumference, i.e. approx.

[14][17] This monument stood in the gymnasium, which was destroyed by fire but was restored with increased magnificence by Pliny the Younger, when he was governor there in the early 2nd century AD.

The Nicene Creed, (Ancient Greek: Σύμβολον τῆς Νικαίας, romanized: Sýmbolon tês Nikaías; Latin: Symbolum Nicaenum; lit.

'Symbol of Nicaea') which declared Jesus to be God, and became the foundation of church doctrine,[20] was adopted at the first Roman Ecumenical Christian council in this city in 325.

[21] This council also condemned Gothic Christian Arianism,[22] which was later adopted by many barbarian kingdoms, and led to the destruction of the Western Empire for the century to come.

However, the city was hit by two major earthquakes in 363 and 368, and coupled with competition from the newly established capital of the Eastern Empire, Constantinople, it began to decline thereafter.

[28] The Seljuk Turks made Nicaea the capital of their possessions in Asia Minor until 1097, when it returned to Byzantine control with the aid of the First Crusade after a one month siege.

Alexios seems to have repaired the aqueduct after the reconquest[29] and major fortifications were constructed across the region, especially by John and Manuel, which helped to protect the city and its fertile hinterland.

There were also several military bases and colonies in the area, for example the one at Rhyndakos in Bithynia, where the emperor John spent a year training his troops in preparation for campaigns in southern Asia Minor.

Although Nicaea was soon abandoned as the primary residence of the Nicene emperors, who favoured Nymphaion and Magnesia on the Maeander, the period was a lively one in the city's history, with "frequent synods, embassies, and imperial weddings and funerals", while the influx of scholars from other parts of the Eastern Roman world made it a centre of learning as well.

The neglect of the Asian frontier by Michael VIII Palaiologos provoked a major uprising in 1262, and in 1265, panic broke out when rumours circulated of an imminent Mongol attack.

[28] Emperor Andronikos II Palaiologos visited the city in 1290 and took care to restore its defences, but Byzantium proved unable to halt the rise of the nascent Ottoman emirate in the region.

[28] After Emperor Andronikos III Palaiologos and John Kantakouzenos were defeated at Pelekanon on 11 June 1329, the Byzantine government could no longer defend Nicaea.

[34] With the fall of Constantinople in 1453, the town lost a great degree of its importance, but later became a major centre with the creation of a local faïence pottery industry in the 17th century.

In most places they are formed of alternate courses of Roman tiles and large square stones, joined by a cement of great thickness.

It seems to have been almost entirely constructed of the remains of the Byzantine-era Nicaea, the walls of the ruined mosques and baths being full of the fragments of ancient Greek, Roman, and Byzantine temples and churches.

Under the shallow waters on the margin of Lake Iznik, at a site still located on firm ground on the lakeshore in Byzantine times, the ruins of a 4th-century basilica were found.