Mount Galesios or Galesion (Greek: όρος Γαλήσιος/Γαλήσιον), today known as Alamandağ or Gallesion in Turkish,^[2] is a mountain north of Ephesus in modern-day Turkey. The mountain is located on the northern bank of the Küçükmenderes River (ancient Kaystros), on the western coast of Asia Minor.^[3] It is notable as the seat of a large Eastern Orthodox monastic community in late Byzantine times, from the 11th century to the area's conquest by the Turks in the 14th century.^[3]

The first monastic community on the mountain was established by the stylite monk Lazaros of Mount Galesios, who died there in 1053.^[4] Already during his lifetime, three monasteries were established near his pillar: the Saviour, reserved for 12 eunuchs; the Theotokos, for 12 monks, and the Resurrection (Anastasis) of 40 monks.^[3] Each had its own hegoumenos (abbot).^[3] A fourth monastery, the Theotokos of Bessai, was established by the imperial family and housed up to 300 monks, but it rapidly declined after the 11th century.^[3] There was also a female convent, that of Eupraxia, where the monks' female relatives could stay.^[3]

The death of Lazaros deprived the community of much of its prestige, but it re-emerged into prominence in the 13th century, with the establishment of the Empire of Nicaea,^[3] when the neighbouring city of Nymphaion became the favourite winter residence of the Nicaean emperors.^[5] The patriarchs Joseph I of Constantinople (1266–1275 and from 1282 to 1283), Gregory II of Constantinople (1283–1289) and Athanasius I of Constantinople (1289–1293 and 1303–1309) were all monks of the "monastery of Galesios"; Gregory II even wrote a new version of the hagiography of St. Lazaros.^[3] The monastery featured a considerable library and a scriptorium.^[3]

The area's history as a monastic centre ended when it was captured by the Turks in the early 14th century.^[3]