The Church of Panagia Acheiropoietos is one of the oldest churches in Thessaloniki, dating back to the 5th century. The existence of a monumental porch on the south side of the church indicates that it was linked with the most important artery in the ancient city, the Leophoras, now Egnatia Street. It is one of the 15 Paleochristian and Byzantine Monuments of Thessaloniki that were included in the UNESCO World Heritage List in 1988. 

The Acheiropoietos is a large Early Christian basilica that is preserved almost to its original height. It was built on a Roman public baths complex, parts of which are preserved outside and beneath the church. In the Early Christian period, the north-east part of the baths seems still to have functioned, and a large room with a niche survives in the north precinct of the church.

The Early Christian basilica is referred to as a church of the Virgin, and indeed as the Great Church of the Virgin, Mother of God, until the 14th century, when the designation Acheiropoietos occurs for the first time in a document dating from 1320. The name is probably to be connected with the cult icon of the Virgin in an attitude of supplication that was kept in the church.

The, Byzantine written sources also reveal that St. Demetrios was worshipped together with the Virgin in the Church of the Acheiropoietos, which may explain the special role played by the church in the procession in honor of the patron saint of Thessaloniki.

After the capture of Thessaloniki by the Turks, Sultan Murad II converted the church into a Muslim house of prayer, called Eski Camii, which remained the official Turkish mosque throughout the entire period of Ottoman rule. The inscription of Murad on the eighth column from the east in the north colonnade of the church is a reminder of the Turkish conquest.

The Acheiropoietos is a three-aisled timber-roofed basilica with galleries. The exonarthex, traces of which can be made out on the west side, was perhaps the east portico of the atrium of the basilica that is probably to be found beneath the modern Makedonomachon Square. The modern roof of the church is lower than the original, because the elevated section of the central aisle, which acted as a light-well, is now missing, as is the west gallery. As a result, the external volume of the church appears even heavier today. Internally, however, the harmony and balance in the articulation of the building, the indirect, diffuse lighting from the multiple windows in the outer walls, and the luxurious, imposing decoration give the church a completely different picture.

At the south end of the west wall of the church, which has a very interesting facade with niches, is the entrance to the narthex, a long, rectangular space occupying the entire width of the nave. The corresponding entrance in the north part of the west wall was blocked up at a later date. The narthex communicates with the side aisles by means of two arched openings. In the middle of its east side is the main entrance to the central aisle, a tribelon formed by two columns of green Thessalian marble. The main aisle is 14.20 m wide and stands in the ratio of 1:2.3 to the side aisles, from which it is separated by two successive colonnades, each with twelve columns of Proconnesian marble. The intercolumniations at ground-floor level were originally blocked with closure slabs in response to liturgical needs. The main aisle ends at the east in the sanctuary, which has large semicircular conch in which are set the synthronon and the bishop's throne. On the exterior, the sanctuary apse has a stepped arrangement. Below the three-light window with pillars, which replaced the original Early Christian five-light window with mullions, are preserved four marble consoles, with the front faces now cut away; these supported the bases of the mullions of the five-light window. The present sanctuary screen is a modern one. The original screen is shown by traces in the floor to have extended to the west as far as the third column from the east.

The north aisle of the church ends at the east at the Middle Byzantine Chapel of Hagia Eirene. In the middle of the south side of the church, to the east of the south porch is an annex, now restored, which is thought to have been the baptistery of the basilica. The original floor of the central aisle, made of large slabs of Proconnesian marble, is still preserved. There is a floor of irregular marble slabs in the chapel of Hagia Eirene and the south aisle. A series of three floors, which can be seen beneath the floor of the north aisle, the first and last with mosaics and the middle one paved with marble slabs, belongs to the earlier, Roman bath-house complex.

In the north precinct of the basilica are traces of a two-storey, vaulted outbuilding, and in the north-west corner is preserved a staircase that led up to the galleries. In its present form, the staircase represents the extensive 7th century repairs that can be detected generally in the basilica alter the earthquake of 620-630. It consists of a main built core and an approach ramp.

The sculptural decoration of the Acheiropoietos consists of a uniform ensemble that was designed and executed for the basilica. The similarity between the Theodosian capitals and the corresponding sculptural members of the Stoudios Monastery in Constantinople (453-454) furnishes a firm date for the monument. The alternating undecorated surfaces, and areas adorned with sawn and acanthus design and the volutes and small leaves on die capitals above the smooth surface of the columns, have reference to a specific aesthetic conception of the Early Christian period.

The same aesthetic conception can be seen in the development of the mural decorative mosaics, which are preserved on the intrados of the arcades on the ground-floor and in the south gallery, on the two large transverse vaults in the narthex, on the tribelon, and on the window in the west wall. The symmetrical, strictly organized development of the decorative motifs projects the religious symbolism of the cross and the scriptures, eucharistic subjects and the paradisal character represented by the vases with water, the birds, fruit and fishes. Traces of a mosaic with a decorative motif are preserved on the west wall of the baptistery.

The mosaics of the Acheiropoietos, like the entire structure of the basilica arid the sculptural decoration, ate probably to be dated to after 450, in the third quarter of the 5th century. This dating is supported by the identification of the donor of the mosaics, Andreas, with the priest Andreas who took part in the Council of Chalcedon (451) as representative of the archbishop of Thessaloniki. The foundation inscription, spread over two blocks, is on the intrados of the south and central arch of the tribelon.

A few wall-paintings in poor condition survive from the Byzantine period of the church, on the wall above the south colonnade. The representation depicts the Forty Martyrs of Sebasteia, who were martyred in the reign of the emperor Licinius. Only eighteen figures of martyrs are preserved, in a rhythmic, linear arrangement. Full-length figures above the columns alternate with busts of martyrs on the surfaces of the wall above the summit of each arch. They are shown wearing military uniform, each holding a cross symbolizing their martyr's death. At either end of the row of martyrs is a candlestick with a lighted candle, a symbolical element found with scenes of a funerary character.

The archaic stylistic features and the stylized expressive means used in the rendering of the figures are survivals of Komnenian art in the painting of the 13th century. In the wall-paintings of the Acheiropoietos, and especially in the faces of the martyrs shown in bust, these characteristics are combined with innovative elements connected with the new cur-rents of renewal in painting, which emerged more fully developed in the monuments of the second quarter of the 13th century. Traces of wall-paintings are also preserved in the Chapel of Hagia Eirine.