The Rotunda of Galerius, was built in the early 4th century AD in Thessaloniki. Subsequently, it served as a church, and its dome was decorated with outstanding Byzantine mosaics.

by Dominik Stachowiak

The center of the second largest Greek city, Thessaloniki, is dominated by a mighty brick round structure with a conical roof – the ancient Rotunda of Galerius. Although its exterior is awe-inspiring, the real treasure – the golden Byzantine mosaics – hides inside. This building witnessed over seventeen centuries of the city’s history and welcomed Roman and Byzantine emperors, Orthodox patriarchs, Turkish imams, and then, Greeks again. Every one of these peoples left a mark which we can read today in the Rotunda.

Rotunda’s Roman Beginnings

It is believed that the Rotunda of Thessaloniki was built at the beginning of the 4th century, probably around AD 305-311, by the Roman emperor Gaius Galerius Valerius Maximianus. The first date is the year when Galerius became augustus of the first Roman tetrarchy and the second is the date of his death. The main reason for attributing the Rotunda to Galerius is its proximity and connection to the palace complex dated with certainty to the times of this emperor. However, another theory dates the building in question to the epoch of Constantine the Great.

The Original Function Of The Building

While the chronology of the building is more or less clear, its initial function is lost in the mists of time. Based on the cylindrical shape and the typological similarity with late antique mausoleums, one theory suggests it to be the gravesite of Galerius, but the fact that he was buried in Romuliana in present-day Serbia contradicts this. Some researchers proposed it to be the planned mausoleum of Constantine the Great, built around AD 322-323 when the emperor was considering Thessaloniki as his new capital. However, the most widely accepted hypothesis views the Rotunda as a Roman temple dedicated either to the imperial cult or Jupiter and Kabyroi.

The small Pantheon of Galerius

The circular shape of the Rotunda brings to mind the 200-year older monument in Rome – the famous Pantheon of Hadrian. Although smaller, the Rotunda is still almost 25 meters in diameter and 30 meters tall. Today, the similarity of the two buildings is not as striking as it must have been in late antiquity, but it must have been obvious to the educated Romans. Certainly, the similarity was not coincidental. In its initial form, the building was much like the Pantheon – a round temple with a monumental porch with columns and a triangular architrave on the southern side. However, unlike the Pantheon, inside the Rotunda were eight 5 meters deep niches, with large windows above them.

The similarities were also obvious in the interior. Between each of the deep niches, there were small niches in the wall, with two columns and a triangular or arched pediment, similar to those in the Pantheon. Probably each of them once housed a marble sculpture. The walls were lined with colorful marbles, just like in other public Roman buildings, but the most striking similarity was seen on the ceiling. In the center of the dome, there was a large circular opening – the oculus. It is not extant today, but its presence is indicated by the details of the dome’s construction and from the circular drain in the middle of the floor, designed to collect the rainwater coming in from the opening. The existence of the oculus indicates that also the conical roof was a later addition, and so the dome must have been visible from the exterior, just like in the Pantheon.

The Imperial Piety And The Conversion Into A Church

Even today the scholars argue over the exact date the Rotunda was turned into a church. While some have proposed the first decades of the 6th century, the shift most likely occurred at some point between the 4th and 5th centuries. The prevalent opinion ties the conversion of the Rotunda with Theodosius the Great, who had been strongly ᴀssociated with Thessaloniki and had visited it many times. He had resided there from January 379 until November 380, then again in 387-388, not counting other, shorter visits. In 388, Galerius had celebrated his decennalia, i.e., ten years of his reign, and married princess Galla in Thessaloniki. This emperor was a true believer who had announced Christianity as the official religion of his empire.

Truly, it is very likely that Theodosius I is the one who converted the Rotunda into a church, in all probability to use it as a palace chapel. To adjust the former Roman temple to its new role, he ordered its extensive rebuilding and redecoration.

The Rotunda As A Palace Church

During the Rotunda’s transformation to a Christian church, the oculus was closed, and the south-eastern niche was enlarged to create an extensive room for the liturgy, with a semicircular apse illuminated by additional windows. Seven other niches were opened to connect it with an extensive, 8-meters wide circular corridor now surrounding the main building. The entire edifice with this addition had a diameter of 54 meters, the same as the Pantheon. In this stage, there were two entrances with antechambers on the south-western and north-western sides. To the first of them, a round chapel and an octagonal annex were attached. The latter served probably as a room for imperial retinue or as a baptistery. Moreover, the interior underwent some significant changes. The small niches between the large ones were closed, the blind arcades at the base of the drum were opened, and the windows in the middle zone were enlarged to compensate for the lack of the oculus as a light source. The dating of this phase is based mostly on the evidence of the brick stamps and the early Byzantine mosaic decoration, which is thought to be contemporary with the closing of the dome.

The Marvelous Byzantine Mosaics

The decoration in the barrel vaults of niches and smaller windows of the dome’s base is purely decorative and mainly lacks deeper theological meaning. The depicted subjects include birds, fruit baskets, vases with flowers, and other images derived from the world of nature. However, most of this space is covered by geometrical motifs. Only three of the early Byzantine mosaics in the barrel vaults are preserved today; the rest of them deteriorated during various earthquakes over the centuries. The decoration of the small windows is very similar in terms of motifs, but the applied color palette is different. While bright colors, such as gold, silver, green, blue, and purple dominate the lower mosaics, in the lunettes, there are darker, pastel colors such as green, green-yellow, lemon, and rose on white marble background. This contrast was created for a particular purpose: the upper mosaics had constant and direct contact with sunlight due to their proximity to windows, and so the colors needed to be darker, while the lower mosaics had only indirect lightning.

The southern niche’s mosaic is exceptional. Its decoration represents a golden Latin Cross with slightly extending ends. It is depicted against the silver-greenish background, surrounded by symmetrically arranged stars, birds with ribbons on their necks, flowers, and fruits. The cross was represented in this particular niche most probably because it led to the palace’s side entrance and its honored emperor.

The Dome Mosaics: The Treasure Of The Early Byzantine Art

The Byzantine mosaics in the dome consisted of three concentric zones, of which only the lowest is fairly well preserved, but the artistry of their makers is unparalleled and has no match even in the famous mosaics of Ravenna. This is also the widest part and the only one that was visible already before the conservation works that took place in 1952 and 1953.

The lowest zone of the Rotunda’s Byzantine mosaics is known as the “martyrs’ frieze”. The main scene of each depiction was placed on an elaborate golden architectural background that reminds the backgrounds of Roman theatre stages, the scenae frons. There are four types of structures arranged so that the building above the eastern niche is pretty much the same structure as the one above the southern niche. The north-eastern panel corresponds with the south-western one and the northern with the western. Also, the north-western panel must have corresponded with the south-eastern one, but the mosaic above the apse was destroyed, and in its place, an Italian artist named S. Rossi painted an imitation of the original in 1889. The mosaics are arranged in pairs symmetrically along an axis marked by the apse and the north-western entrance, dedicated to the ecclesiastical ceremonies.

In front of the architectural background, there are 15 (originally 20) male figures identified by inscriptions as martyrs. Their images are idealized. For example, saints known as hermits are as elegant and dignified as bishops. The saints are represented in this certain way, highlighting their spiritual power, peace and beauty, because they are no longer troubled with earthly matters, but live in the golden city of Heavenly Jerusalem, and their bodies are celestial and not earthly. Their appearance reflects their internal beauty, values, and perfection in the eyes of the early Christians.

The middle zone of the dome mosaic is regrettably nearly completely lost, and the only preserved remains are just some kind of short grᴀss or bushy plant, a few pairs of sandaled feet, and edges of long white cloths. Those belonged possibly to 24 to 36 figures depicted in motion, grouped in three. They were identified variously as prophets, saints, or more possibly as twenty-four Elders or angels adorning Christ.

These marvelous Byzantine mosaics were executed in small tesserae, that is, glᴀss or stone cubes, of various colors. An average one covers about 0.7-0.9 cm2, and the whole dome program covered approximately 1414 m2. Since one mosaic cube weighs about 1-1.5 g, it is estimated that the entire dome mosaic weighed about seventeen tones (!), of which roughly thirteen tones were made of glᴀss.

Angels, Phoenix And Christ – The Dome’s Medallion

The last part of the mosaic decoration, located in the very apex of the dome, is the medallion held by four angels, with a phoenix – an ancient symbol of resurrection – between the two of them. The medallion is relatively well preserved and consists of: (from the outside) a rainbow ring, a rich band of vegetation with twigs and leaves of different plants, and a blue band with fourteen preserved stars. Inside this circle, there used to be a depiction of a youthful Christ holding a cross. Only a fraction of the halo, the fingers of his right hand, and the top of his cross are preserved. Fortunately, there is a charcoal sketch in the missing part of the figure that once served the artisans laying out the mosaic. Today, this sketch allows the mosaic’s reconstruction.

The overall theological representation of the dome’s early Byzantine mosaics is that of the heavens with the golden city of the Heavenly Jerusalem known from the Apocalypse, then upper in the heavenly hierarchy the angels or the Elders, and in the center Christ himself.

The Apse Painting

In the middle Byzantine period, around the 9th century, after the iconoclasm, there was a scene of Ascension painted in the semidome of the apse. The painting is divided into two horizontal zones. On the upper one, Christ is seating within a yellow disc supported by two angels in bright garments. Directly below the Christ, Virgin Mary stands with her hands raised in prayer. She is surrounded by two angels and the Apostles. Above them is an inscription with the text of a gospel. This composition is characteristic of Byzantine Thessaloniki and probably repeats the same scene from the dome of Thessaloniki’s Hagia Sophia, the local cathedral that should not be confused with the Hagia Sophia of Constantinople.

Occupation And liberation: The Post-Byzantine History Of The Rotunda

In 1430 Thessaloniki was captured by the Ottoman Empire and many of its churches were converted into mosques. In 1525 this fate was also shared by the cathedral of Hagia Sophia, leaving the Episcopal center’s role to the Rotunda. This situation lasted only until 1591 when by the order of sheikh Hortaçlı Süleyman Efendi it was given to an order of Muslim dervishes as a mosque. In that period, a slim minaret was erected, the only one that survived the recapturing of the city by the Greeks in 1912, and preserves in full height until today.

It is noteworthy that the lower mosaics of the dome, with the Christian theme of the Heavenly Jerusalem, were not covered by the Turks during the building’s time as a mosque, unlike the apse’s fresco.

In 1912, the Rotunda was converted into a church once again after over 300 years, but its original Byzantine name had already been forgotten, and the temple ᴀssumed the name of St. George, which it bears until today. In 1952 and 1953, and then again in 1978 the mosaics were restored after a major earthquake that stroke Thessaloniki. Presently the Rotunda is available to visitors as a UNESCO heritage site but also serves as an Orthodox church on every first Sunday of the month.