At the beginning of Olympus street, very close to the western limb of the walls of Thessaloniki, it stands the church of Agioi Apostoloi, one of the finest and most important monuments of the city. As evidenced by the remains of an imposing bell pillar and a large cinstern (water reservoir), the temple was originally the cathedral of an extensive and rich monastic complex, which - according to a dedicatory inscription - was erected between 1310 and 1314 sponsored by Patriarch Nifon A. However, this monastery (and its cathedral, by extension), as indicated by the Panagia’s scenes of the painting decoration of the temple was apparently built in honor of Panagia (this could be probably the Monastery of Panagia Gorgoepikoos). The church later was dedicated to Agioi Apostoloi, because of the popular belief that it was covered with twelve arches that symbolized the twelve Apostoloi. Between 1520 and 1530 the monument was converted into a muslim mosque and was renamed into Soğuk Su mosque.
The temple of Agioi Apostoloi is a complex four-columned registered cruciform with ambulatory in western, southern and northern side, which in the eastern ends in chapels; also on the western side there is shaped an outer narthex while the east is dominated by a large central seven-sided arch, which is flanked by two smaller three-sided niches. The building has five domes, one large and elevated in the center and four smaller and lower in the corners.The proportions of the building are very harmonious, refined and slender, the organization of space, the structure of surfaces, the division of tumors and the escaling levels were made with inspiration and wisdom, while the ceramic-plastic decor - especially on the east side - is very rich. Undoubtedly, the architect of the monument has created a light and elegant composition, distinct from beauty, grace and uplift.
The painted decoration of the church of Agioi Apostoloi, despite the damage and the fragmentary state of its preservation, is brilliant, characterized by unmatched quality and constitutes a benchmark for the Byzantine art of the early 14th century. The higher parts of the nave were decorated with mosaic masterpieces, which constitute one of the last sets of such decoration in Byzantium, before starting the downturn of the empire. Main attributes of them are kindness, the classical concept and the trend towards realism in setting and shaping the figures, the depiction of emotions in faces, the feeling of third dimension, the monumental mood. The artwork of the building was completed with extensive wall paintings of great artistic value, which - among others - depict saints’ figures, scenes from the Old and New Testament, episodes from the life of Panagia and Ioannis the Prodrome,as well as themes inspired by hymnological texts.