Akdamar Island (also known as Aghtamar, Akhtamar, and Aght'amar; Turkish: Akdamar Adası; Armenian: Ախթամար, Armenian pronunciation: [ɑχtʰɑmɑr]) is a small island in Lake Van in the Eastern Anatolia region of Turkey, about 0.7 km² in size, situated about 3 km from the shoreline. At the western end of the island a hard, grey, limestone cliff rises 80 m above the lake's level (1,912 m above sea level). The island declines to the east to a level site where a spring provides ample water. It is home to a tenth century Armenian church, known as the Cathedral Church of the Holy Cross (915-921), and was the seat of an Armenian Catholicos from 1116 to 1895.

The architecture of the church is based on a form that had been developed in Armenia several centuries earlier; the best-known example being that of the 7th century St. Hripsime church in Echmiadzin, incorporating a dome with a conical roof.

The unique importance of the Cathedral Church of the Holy Cross comes from the extensive array of bas-relief carving of mostly biblical scenes that adorn its external walls. The meanings of these reliefs have been the subject of much and varied interpretation. Not all of this speculation has been produced in good faith - for example, Turkish sources stress alleged Islamic and Turkic influences behind the content of the reliefs and minimise native Armenian influences. Some scholars assert that the friezes parallel contemporary motifs found in Umayyad art - such as a turbaned prince, Arab styles of dress, wine imagery; allusions to royal Sassanian imagery are also present (Griffins, for example).