From Pagan Rome to Christian Byzantium: What Changed, When, and What You Can Still See in Thessaloniki

The political events that made Christian Byzantium possible

The Edict of Milan in 313 AD is often cited as the beginning of the transition, but its practical impact was more limited than its reputation suggests. It extended religious toleration to Christians alongside practitioners of other religions; it did not make Christianity the state religion.

The decisive step came in 380 AD with the Edict of Thessaloniki — issued, significantly, from this city by Emperor Theodosius I — which declared Nicene Christianity the sole legitimate religion of the Roman Empire and redefined all other religious practices as heresy.

The edict was issued from Thessaloniki specifically because Theodosius was based there during his campaigns against the Goths, making the city the administrative centre from which Christian Byzantium was legally constituted. The practical enforcement of Theodosius’s edict took decades.

Temple closures, the abolition of the Olympic Games (393 AD), the seizure of temple properties and their conversion to church use — all of these proceeded unevenly across the empire. In Thessaloniki, the process is archaeologically documented in the conversion of several Roman-era civic buildings and temples to Christian use between the late 4th and early 5th centuries.

The site beneath the Basilica of Agios Dimitrios, excavated during the 20th-century restoration, revealed Roman bath structures from the 3rd century; the saint’s martyrdom is dated to approximately 306 AD within those structures.

The visual transformation: what changed in art and architecture and why

Roman art of the 1st and 2nd centuries AD operated within a coherent system of visual conventions derived from classical Greek practice: naturalistic human proportions, illusionistic depth, narrative scenes organised spatially in real or implied landscape settings. The transition to Christian Byzantium did not immediately discard this system but progressively subordinated it to a different set of priorities.

The shift is legible in a sequence of dateable objects: compare a Roman portrait bust from the 2nd century with a 4th-century Christian sarcophagus relief, and then with a 6th-century icon. Each step away from naturalism toward symbolic abstraction corresponds to a step toward the Byzantine visual theology described in more detail in this site’s guide to Byzantine icons.

The architectural transition followed a parallel but distinct path. The building type that Christian Byzantium adopted as its primary ecclesiastical form — the basilica — was not a pagan temple. Roman temples were closed structures housing a cult image, not designed for congregational worship.

The basilica was a Roman civic building type used for markets, law courts and public assembly: a long rectangular hall with a central nave flanked by side aisles, terminated by a semicircular apse. Its adoption by the Christian Church was a deliberate choice of a secular rather than a sacred building type, which allowed Christian architects to adapt it without directly competing with or replicating pagan temple architecture.

The Panagia Acheiropoietos in Thessaloniki, built around 450–470 AD, is among the earliest surviving examples of this type with its original structural fabric largely intact.

How pagan symbols were reinterpreted in Christian Byzantium

The reuse of pagan visual motifs in Christian contexts was systematic rather than accidental. Vine scrolls, which in Roman art represented abundance and the pleasures of the physical world, appeared in Early Christian basilica floor mosaics as symbols of the Eucharistic wine and of the Church as a living organism — a reinterpretation authorised by Christ’s description of himself as “the true vine” in John 15:1.

The peacock, a symbol of immortality in both Roman and Near Eastern traditions, appeared in Christian funerary art from the 3rd century onward as a symbol of resurrection. The Good Shepherd figure — a young man carrying a sheep on his shoulders — derived directly from the Hermes Kriophoros (ram-bearer) of Greek sculpture, but was reread as Christ the shepherd of souls.

These borrowings were not theologically neutral. They were the result of a deliberate programme of cultural appropriation that allowed Christianity to communicate within the existing visual vocabulary of the Roman world while redirecting that vocabulary toward new ends.

The Museum of Byzantine Culture’s Rooms 1 and 2 present this process through a sequence of objects in which the transition is visible within individual pieces: a 4th-century marble relief showing the Good Shepherd in a posture indistinguishable from its Hermes Kriophoros model, surrounded by vine scrolls that could belong to either tradition, framing a clearly Christian chi-rho monogram. Both visual languages inhabit the same object simultaneously.

From Rome to Byzantium: what you can see on foot in Thessaloniki

The most compressed physical sequence of the Rome-to-Byzantium transition in Thessaloniki runs along approximately 400 metres of the ancient Decumanus Maximus, the Roman city’s principal east-west street, which survives as the axis between Navarino Square and the Rotunda.

Starting at the Arch of Galerius — a pagan triumphal monument of 298–305 AD with carved reliefs of military campaigns and pagan sacrifice scenes on its piers — and walking 300 metres east to the Rotunda, you cover the physical span of the transition in a single short walk.

The Arch was built to celebrate a pagan emperor. The Rotunda it was aligned with was built as a pagan structure and converted to a Christian church within a century. Both still stand within sight of each other. The Rotunda’s interior — open Tuesday to Sunday 08:00 to 15:00 in winter, entry €6 — contains surviving 4th-century mosaic decoration in the drum at the base of the dome.

The mosaics, produced after the building’s conversion to Christian use around 400 AD, show saints standing in architectural niches against a gold background: the earliest large-scale gold-ground mosaic programme in the city and one of the earliest surviving examples of the Christian Byzantium visual system at monumental scale.

The contrast between the pagan military reliefs on the Arch of Galerius outside and the Christian gold mosaics inside the Rotunda 300 metres away compresses the entire theological and visual transformation of the empire into a single walk.

How the Museum of Byzantine Culture presents the transition

The Museum of Byzantine Culture on Stratou Avenue organises its first three rooms specifically around the transition from Late Roman to Early Christian visual culture, making it the most systematic indoor presentation of the Rome-to-Byzantium shift available in the city.

Room 1 opens with Roman-period architectural fragments — marble capitals, carved column bases, floor panel sections — and traces the shift in decorative vocabulary from classical to Christian motifs within the same building types. Room 2 addresses Early Christian funerary practice, where the reinterpretation of Roman funerary imagery (the orans figure, the vine scroll, the shepherd) is directly visible in datable objects.

Room 3 contains the 5th-century floor mosaic fragment that shows the Christian Byzantium iconographic programme fully established. The museum is open Tuesday to Sunday from 08:00 to 15:00 in winter (08:00 to 20:00 April through October), closed on Mondays; admission is €8 for adults, free for visitors under 18 and EU citizens over 65.

A combined ticket covering the Byzantine Museum, Archaeological Museum, White Tower and Rotunda costs €15 and is the most practical option for visitors planning to cover the full sequence described in this article across both indoor and outdoor sites. The sequence — museum in the morning, Rotunda and Arch of Galerius on foot in the afternoon — covers the Rome-to-Byzantium transition in roughly five hours with no transport required.

What survived from Rome into Christian Byzantium and why it matters

The conventional narrative of the fall of Rome presents the transition as rupture: one civilisation ending, another beginning. The physical and documentary evidence from Thessaloniki tells a more complicated story. Roman administrative structures — the provincial system, the urban magistracies, the legal corpus — survived into the Byzantine period largely intact.

The Greek language, which had been the administrative and cultural language of the eastern empire since the Hellenistic period, became the official language of the Byzantine state under Heraclius (r. 610–641 AD), formalising a reality that had existed for centuries.

Roman law was codified and preserved in Justinian’s Corpus Juris Civilis (529–534 AD), which remains the foundation of civil law systems across Europe, including Greece, today. What the transition to Christian Byzantium changed was not the institutional framework of the Roman world but its orientation: from a cosmology centred on the visible, the measurable and the political, to one centred on the invisible, the theological and the eschatological.

The art and architecture visible in Thessaloniki’s churches and the Museum of Byzantine Culture are the material record of that reorientation — not a replacement of Rome, but Rome’s deliberate and systematic transformation of itself into something that could last another thousand years.