Trebizond (Tραπεζούς, modern Trabzon/Turkey) was the most important city of the Pontos. It flourished because of its fine harbor and location at the head of the best route from the sea to the interior and Persia. Restored by Diocletian after a Gothic attack, Trebizond became a legionary base and a city of Pontos Polemoniakos. In the reorganization of Justinian I, it was assigned to Armenia I. Justinian conducted his Armenian campaigns from Trebizond, restored its walls, and built an aqueduct. Trebizond had bishops from the 3rd century onward; Eirenaios, responsible for the rebuildings of Justinian, played a major role in civic life. Trebizond became an archbishopric in the 8th century and a metropolis of the diocese of Lazike in the early 10th century. In the 7th century, Trebizond became a city Of Armeniakon, and, in the early 9th century, capital of Chaldia. A brief Turkish occupation after 1071 was followed by the rule of the Gabrades, nominally subject to the Komnenoi. The well-documented period after 1204 was one of great architectural and artistic activity.

The Empire of Trebizond, based in the city of Trebizond, was one of the three successor states to the Byzantine Empire, lasting from 1204 to 1461. It arose at the time of the conquest of Constantinople by the Fourth Crusade. Unlike the empire of Nicaea and despotate of Epiros, however, the empire of Trebizond was established not in response to the Latin occupation, but just prior to it as a continuation of the rule of the Komnenian dynasty, overthrown in 1185 by the Angeloi. Founded by Alexios II Komnenos and David Komnenos, grandsons of Andronikos I Komnenos, the new "empire" was restricted to a narrow strip of land along the southeast coast of the Black Sea and was isolated from Constantinople. Under the rule of the Grand Komnenoi, the empire of Trebizond survived for 250 years, despite its small size and the constant threat of conquest by the Turks. Its longevity can be attributed to the natural barrier of the Pontic Mountains, the strong fortifications of the capital city, the flourishing commerce of this port city, and the astute marriage diplomacy carried out by the Trapezuntine emperors, who sought alliances for themselves primarily with Byzantine and Georgian princesses and married many of their daughters and sisters to Turkomans. For much of its history the empire was the vassal of successive stronger powers: the Seljuks of Ikonion (1214-43), the Mongols (after the invasions of 1243 and 1402), and the Ottomans (after 1456). It was the last outpost of Byzantine civilization to fall to the Turks, being forced to surrender in 1461 when besieged by Ottoman forces by land and sea.

In 1204, Trebizond consisted of a small fortified enceinte on a steep hill, with market, harbor, suburbs, and separately fortified monasteries outside the walls. Much of it was exposed to Turkish attacks, which began in 1223. Alexios II Komnenos, emperor of Trebizond (1297-1330), built a new wall that encompassed the harbor and lower city. It was strengthened in 1378; the citadel, which contained the imperial palace and government offices, was frequently repaired until the fall of the Trapezuntine Empire. The commercial district, with numerous churches and the separate fortifications of the Genoese and Venetians, lay beyond the walls. Names of many quarters are known from contemporary texts or later Turkish documents. In spite of its numerous monuments, Trebizond was surprisingly small, with only about 4,000 inhabitants in 1438. Powerful fortifications and an isolated location enabled it to survive numerous Turkish attacks until 1461.

Monuments of Trebizond include the fortifications, which manifest eight periods of construction, mostly of the 13th-14th century. Parts of the palace have also survived. Trebizond preserves the remains or memory of some 95 churches. Most important is the monastery of Hagia Sophia, probably founded by Manuel I Komnenos, emperor of Trebizond (1238-63), and extensively rebuilt in the early 15th century; a cross-in-square church with three apses, a narthex, and three porches, its interior was covered with frescoes. Also prominent are the Church of St. Eugenios of Trebizond (1291); the Cathedral of Panagia  Chrysokephalos, rebuilt in 1214 as the imperial coronation church; and the earliest church of Trebizond, the Basilica of St. Anne, restored in 885. Other churches are generally small and undatable, but their characteristic pentagonal apses and porches suggest that most belong to the period of the 13th-15th century.