A 14th-century Byzantine church, part of UNESCO's Paleochristian and Byzantine Monuments of Thessalonika. It appears that the church was originally built as the katholikon of a monastery. The founder's inscription above the entrance, the monograms in the capitals and other inscriptions refer to Nephon I, Patriarch of Constantinople in 1310-1314, as the ktetor. Recent analysis using carbon-14 however points to a later date for the entire structure, ca. 1329. A series of Marian scenes lead to the conclusion that the church was dedicated to the Virgin, perhaps to be identified with the Monastery of Theotokos Gorgoepikoos. With the conquest of the city by the Ottoman Turks, in ca. 1520-1530 the church was converted into a mosque with the name Soğuksu Camii ("Mosque of the Cold Water"). As was their usual practice, the Ottomans covered the mosaics and frescoes with plaster. Restoration of the frescoes began in 1926. The church's modern name, "Holy Apostles", was not attributed to the building until the 19th century.