The Church of the Holy Apostles is a 14th-century Orthodox church in the northern Greek city of Thessaloniki. The church is located at the start of Olympou Street, near the city's western medieval walls.
As evidenced by remnants of a column to the south of the church and a cistern to its northwest, it originally formed part of a larger complex. Consequently it appears that the church was originally built as the katholikon of a monastery.
The date of its construction is not entirely clear: 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 founder. Another inscription on the eastern wall commemorates the same patriarch and his pupil, the abbot Paul, as first and second founders respectively. Recent analysis using carbon-14 however points to a later date for the entire structure, ca. 1329. Patriarch Nephon I there was probably a benefactor, and therefore considered a founder.
A depiction of the abbot Paul kneeling before the Virgin Mary, as well as a series of Marian scenes lead to the conclusion that the church was dedicated to the Virgin Mary, perhaps to be identified with the Monastery of Theotokos Gorgoepikoos.
The building belongs to the type of the composite, five-domed cross-in-square churches, with four supporting columns. It also features a narthex with a U-shaped peristoon (an ambulatory with galleries), with small domes at each corner. There are also two small side-chapels to the east. The exterior walls feature rich decoration with a variety of brick-work patterns.
The interior gives a very vertical impression, as the ratio of height to width of the church's central bay is 5 to 1. The interior decoration consists of rich mosaics on the upper levels, inspired by Constantinopolitan models. These are particularly important as some of the last examples of Byzantine mosaics (and the last of its kind in Thessaloniki itself). Frescoes complete the decoration on the lower levels of the main church, but also on the narthex and one of the chapels. These too show influence from Constantinople, and were possibly executed by a workshop from the imperial capital, perhaps the same which decorated the Chora Church. They were probably carried out under the patronage of the abbot Paul, after 1314 or in the period 1328–1334.
The mosaics of the Holy Apostles — one of the last examples of this kind of decoration in the Byzantine Empire — are, along with the corresponding depictions in the Chora Monastery and the Church of the Pammakaristos in Constantinople, the supreme examples of the art of the Palaiologan period. Their strong recollections of Hellenistic elements, discernible in the treatment of the bodies and clothes, their rendering of feelings in the faces, and their tendency towards realism are all features distinguishing them from the idealistic works in the capital. The wall-paintings completing the decoration of the katholikon are of equally high quality.
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"), due to the cistern next to it. As was their usual practice, the Ottomans covered the mosaics and frescoes with plaster, after they removed the gold tesserae. The church's modern name, "Holy Apostles", was not attributed to the building until the 19th century. It owes its modern name to the popular belief that the church was once roofed with twelve domes symbolizing the apostles.
Restoration and the gradual revealing of the frescoes began in 1926. After the 1978 earthquake, the building was strengthened, and in 2002, the mosaics were cleaned up.
