The oldest surviving Christian text is a letter addressed to a Balkan city. Written around 50 or 51 AD, probably from Corinth, Paul’s first letter to the Thessalonians predates every Gospel, every other epistle, every fragment of Christian literature that has reached us. The very first words of organized Christianity that survive in writing were addressed to a small community in what is now Greece’s second city.
This is not widely appreciated. The standard narrative of early Christianity runs through Jerusalem, Antioch, and Rome. The Balkans get a footnote: Paul passed through on his way somewhere important. But the actual record tells a different story.
Paul established his first European church in Philippi, a Roman colony in eastern Macedonia, around 49 or 50 AD. He wrote to the Thessalonians from Corinth a year or two later. The emperor who legalized Christianity, Constantine, was born in Naissus, modern Niš in Serbia. The edict that made Nicene Christianity the state religion of the Roman Empire was issued from Thessaloniki in 380 AD. The council that produced the first formal East-West split in Christian history met at Serdica, modern Sofia, in 343 AD. And the man who transmitted Christianity to the entire Germanic world did it from Nicopolis ad Istrum, a town in northern Bulgaria, using an alphabet he invented for the purpose.
The Balkans were not on the margins of early Christianity. They were the arena where it was fought over, defined, and transmitted. Then, in the catastrophe of the 6th and 7th centuries, almost everything that had been built was destroyed. When Christianity returned to the same territory two hundred years later, it came through different missionaries, in different languages, to different peoples. And the region that had received Christianity first became the fault line where it split.
Paul and the Road
Paul traveled the Via Egnatia, the main Roman highway connecting the eastern Mediterranean to the Adriatic coast. Built between 146 and 120 BC, the road ran approximately 1,120 kilometers from Dyrrachium (modern Durrës in Albania) to Byzantium, passing through Thessaloniki, Amphipolis, and Philippi along the way. It was the backbone of Roman military and commercial movement in the region. Paul used it as his missionary highway.
He arrived at Philippi around 49 or 50 AD, on what is conventionally called the Second Missionary Journey. Acts 16 describes what happened there, and Paul’s own letter to the Philippians confirms some of it.
Philippi had no synagogue. This is telling. Jewish law required ten adult males for a synagogue to be established. A Roman colony of military veterans, Philippi apparently did not have even that many Jewish residents. Paul found a small group, mostly women, meeting for prayer by the river Gangites outside the city walls. Among them was Lydia, a dealer in purple cloth from Thyatira in Asia Minor. She was the first documented European convert to Christianity.
What happened next is one of the more dramatic passages in Acts. Paul exorcised a fortune-telling slave girl, which cost her owners their revenue stream. They had Paul and Silas arrested, beaten with rods, and thrown into the inner prison with their feet in stocks. That night, an earthquake shook the foundations, the doors flew open, and every prisoner’s chains came loose. The jailer, assuming his prisoners had escaped (a death sentence for him), was about to kill himself when Paul called out from the darkness. The jailer and his entire household were baptized before dawn.
Paul’s own letter to the Philippians remembers none of this drama. What he remembers is the pain (“we had already suffered and been shamefully treated at Philippi,” 1 Thessalonians 2:2) and the generosity. The Philippians were the only church that supported Paul financially from the very beginning, sending money even after he had moved on to Thessaloniki.
From Philippi, Paul followed the Via Egnatia west to Thessaloniki, the provincial capital of Macedonia. Here he found a synagogue and preached on three consecutive Sabbaths. Some Jews, many Greeks, and “not a few” prominent women were persuaded. The opposition came quickly. A mob attacked the house of Jason, who had been hosting Paul, and dragged Jason before the city authorities. The charge was political, not theological: “These men are acting against the decrees of Caesar, saying there is another king, Jesus.”
The accusers used the word “politarchs” for the city officials. For centuries, critics of Acts considered this term an error, since it appeared nowhere else in classical literature. Then, in 1876, workers demolishing Thessaloniki’s Vardar Gate discovered an inscription bearing the word “politarchai.” The inscription is now in the British Museum. Over sixty politarch inscriptions have since been found, three-quarters of them from Macedonia.
Paul left Thessaloniki under pressure and went south to Beroea (modern Veria), where Luke records that the Jews were “more noble-minded” because they checked Paul’s claims against scripture daily. When opponents from Thessaloniki followed him there, Paul moved on to Athens, and eventually to Corinth.
It was from Corinth, around 50 or 51 AD, that Paul wrote his first letter to the Thessalonians. Not a Gospel, not a systematic theology, but a personal letter to a small community in a provincial capital, written by a man who had been run out of town, reassuring them about the fate of believers who had died before Christ’s return. The date is anchored by archaeology: an inscription found at Delphi in 1905 dates the proconsulship of Gallio in Achaia to approximately mid-51 to mid-52 AD. Acts 18 records Paul being brought before Gallio in Corinth. This is the single most important fixed date in Pauline chronology. Everything else is calculated relative to it.
“As Far as Illyricum”
Paul made one claim about the western extent of his mission that remains debated. In Romans 15:19, written from Corinth around 56 or 57 AD, he states: “From Jerusalem all the way around to Illyricum, I have fully proclaimed the gospel of Christ.”
The Greek is ambiguous. The word mechri (“as far as”) can mean “up to the border of” or “into.” Whether Paul actually entered Illyricum or merely reached its eastern edge is grammatically unresolvable. If he did enter, the most likely time was during the Third Missionary Journey (around 55-56 AD), when his movements are less fully documented by Acts. Geographically, Illyricum covered the eastern Adriatic coast, encompassing parts of modern Croatia, Bosnia, Montenegro, Albania, and Serbia.
A separate reference appears in 2 Timothy 4:10, where Paul mentions that Titus has gone to Dalmatia. Dalmatia was the updated Roman name for southern Illyricum, in use from the Flavian period onward. Whether this reflects an established Christian community or a fresh mission is unclear. The Pastoral Epistles (1 Timothy, 2 Timothy, and Titus) are among the most disputed texts in the New Testament, with many scholars considering them pseudepigraphic. If they are genuine, they place active Christian work along the eastern Adriatic coast by the early 60s AD.
Church tradition extends the apostolic reach further. Origen, writing in the early 3rd century (preserved through Eusebius, Church History III.1), records that “Scythia was allotted to Andrew.” The apocryphal Acts of Andrew (late 2nd century) elaborates this into a Black Sea mission. The tradition that Andrew founded the Bishopric of Byzantium is demonstrably later: Francis Dvornik’s definitive study (Harvard, 1958) found no trace of it before the end of the 6th or beginning of the 7th century. The motivation was political: giving Constantinople an apostolic founder to rival Rome’s Peter.
The honest picture: Paul’s Macedonian mission is documented in both Acts and his own letters. His reach into Illyricum is plausible but unconfirmable. Andrew’s Black Sea mission rests on tradition first recorded at least 150 years after the fact. The further west and north we go from the Via Egnatia, the thinner the evidence becomes.
The Blood Price
For two and a half centuries after Paul, Christianity spread through the Balkans with the usual mix of quiet growth and periodic violence. The great persecutions under Decius (250-251) and Valerian (257-258) produced Balkan victims, but the documentary record is thin. It is with Diocletian’s persecution (303-311), the last and most systematic Roman assault on Christianity, that the Balkans come into sharp focus.
Diocletian had strong Balkan connections. He was born near Salona in Dalmatia (modern Split) and built his retirement palace there, an enormous fortified complex where he intended to grow cabbages in peace. The persecution he ordered was enforced with particular severity in the regions closest to the imperial centers, and Sirmium, one of the four Tetrarchy capitals, was among the hardest hit.
Bishop Irenaeus of Sirmium was arrested in 304 AD. His Passio, classified among the acta sincera (martyrdom accounts considered historically reliable, free of legendary embellishment), records what happened in remarkable detail. Irenaeus was young, married, with children. He was brought before the provincial governor Probus and ordered to sacrifice to the Roman gods. He refused. His family came to the prison and begged him to comply. He refused again. After being beaten with clubs, he was presented to Probus at midnight. Still refusing, he was sentenced to death.
On April 6, 304, Irenaeus was led to the Pons Basentis, a bridge over the Sava River. He removed his clothes, raised his hands in prayer, and was beheaded. His body was thrown into the river. His deacon Demetrius was martyred the following day. This Demetrius may, according to the Bollandist scholar Hippolyte Delehaye, be the historical kernel behind the later cult of Saint Demetrius of Thessaloniki, which would make one of the most venerated saints in Eastern Christianity originally a Sirmian deacon, not a Thessalonikan soldier.
Sirmium was not alone. At Salona, Bishop Domnius was executed on April 10, 304. Archaeological confirmation of his cult exists at the Manastirine cemetery outside the city walls. At Thessaloniki, three sisters named Agape, Chionia, and Irene were arrested in April 304 for possessing Christian scriptures. Their trial records appear to preserve elements of actual judicial protocol. At Durostorum (modern Silistra, Bulgaria), a concentration of soldier-martyrs fell between 303 and 307, including Dasius, who was beheaded for refusing to play the role of mock-king in the Saturnalia festival.
The most extraordinary aftermath belongs to Diocletian’s own palace. When Salona was destroyed by Avars and Slavs around 614, the surviving Christian population fled to the nearest defensible structure: the emperor’s retirement palace in Split. They settled inside the walls and converted his mausoleum into the Cathedral of Saint Domnius, named after the bishop Diocletian himself had executed three centuries earlier. The mausoleum’s original function is still visible in its architecture. It is the oldest Catholic cathedral building still in use in its original structure.
The Emperor from Niš
The Balkans did not merely receive Christianity. They produced the man who made it legal.
Constantine was born in Naissus, modern Niš in central Serbia, around 272 AD (the exact year ranges in scholarship from 271 to 273). His father, Constantius Chlorus, was a Roman military officer who would become Caesar of the Western Roman Empire. Constantine grew up in the Balkan military culture that had been producing emperors since the crisis of the 3rd century.
He was not unique in this. The phenomenon of “Illyrian emperors,” soldiers of humble Balkan origin who rose through the ranks to seize the purple, is one of the most striking features of late Roman history. At least twenty emperors of Balkan origin ruled between 268 and 565 AD. Claudius Gothicus came from Sirmium or its vicinity. Aurelian came from Dacia Ripensis. Diocletian came from Salona. Galerius came from Gamzigrad in eastern Serbia. Valentinian I came from Cibalae (modern Vinkovci, Croatia). Justin I came from near Naissus. Justinian I came from Tauresium, near modern Skopje.
The Danube frontier was the empire’s most active military zone. It produced tough, practical soldiers who knew how to fight, how to command, and how to seize power. When the empire’s center of gravity shifted from the Italian senatorial aristocracy to the professional military, the Balkans supplied the men who ran it.
Constantine’s contribution to Christianity needs no lengthy retelling. The Edict of Milan (313) granted legal tolerance to all religions. The Council of Nicaea (325) produced the first empire-wide creed. Whether Constantine was a sincere convert, a political pragmatist, or something more complicated is a question the sources do not fully answer. What is clear is that the man who set Christianity on its path to becoming the dominant religion of the Western world was born in a medium-sized Balkan city.
The archaeological site of Mediana, four kilometers east of Niš, preserves the kind of imperial residence where Constantine likely spent part of his youth. Two early Christian churches at the site date to around 378 AD, and the Jagodin Mala necropolis nearby has yielded over sixty-five brick-lined tombs with Christian wall paintings.
Where East First Met West
The 4th century is when the Balkans became Christianity’s theological arena. The controversy over Arianism, the question of whether Christ was of the same substance as the Father or merely similar, was not decided in Rome or Alexandria or Constantinople. It was fought, council by council, in the cities of the Balkans.
The Council of Serdica in 343 AD was supposed to resolve the crisis that had been tearing the church apart since Nicaea. Over 170 bishops traveled to Serdica, modern Sofia, for a joint East-West council convened by the emperors Constans and Constantius II. It was a disaster.
The Western bishops, led by Hosius of Cordoba, demanded that the exiled Athanasius of Alexandria and Marcellus of Ancyra be seated as full participants. The Eastern bishops refused. They would not sit in council with men they had already deposed. After days of failed negotiation, the Eastern delegation walked out entirely and traveled to Philippopolis (modern Plovdiv, about 150 kilometers southeast), where they held their own counter-synod. The two groups never met as one body.
The Western rump council issued twenty canons, including one asserting the right of bishops to appeal to Rome. The Eastern counter-synod excommunicated the Western leaders. Serdica did not solve the Arian controversy. It produced the first formal East-West split in Christian history, a preview, seven centuries early, of what would become permanent in 1054.
The arena then shifted to Sirmium. Between 347 and 378, at least five church councils met in this Balkan capital, all wrestling with the same question: how to define the relationship between the Father and the Son. The theological factions produced competing creeds at an exhausting rate.
The key figures were two Balkan bishops: Ursacius of Singidunum (Belgrade) and Valens of Mursa (modern Osijek, Croatia). Both had been disciples of Arius himself during his exile in Illyricum after the Council of Nicaea. They became the most influential Arian bishops in the empire. After the Battle of Mursa in 351, where Constantius II defeated the usurper Magnentius, Valens became Constantius’s spiritual director. This gave Balkan Arianism direct access to the emperor.
The peak came in 357. The Third Council of Sirmium produced a creed that explicitly banned the use of both homoousios (same substance) and homoiousios (similar substance), effectively prohibiting any discussion of divine substance at all. Hilary of Poitiers called it the “Blasphemy of Sirmium.” Jerome captured the moment in a famous line: the whole world groaned and was astonished to find itself Arian.
The Arian position would ultimately lose. Theodosius I ended the controversy by imperial decree in 380. But for three decades, the theological center of Christianity was not Rome or Constantinople. It was the council halls of Sirmium and the episcopal residences of Belgrade and Osijek.
One Man, One Bible, One Alphabet
While bishops fought over creeds in Sirmium, one man was doing something more consequential from a Roman city in northern Bulgaria.
Wulfila (also spelled Ulfilas) was born around 311 AD among the Goths living north of the Danube. His ancestors, parents or perhaps grandparents according to Philostorgius, had been Cappadocian Christians captured by Gothic raiders. He was consecrated as bishop by Eusebius of Nicomedia, an Arian, around 341 AD, and sent to evangelize the Goths.
After seven years of mission work north of the Danube, persecution by the Gothic chieftain Athanaric forced Wulfila and his community to cross into Roman territory. Emperor Constantius II settled them near Nicopolis ad Istrum in Moesia Inferior, in what is now northern Bulgaria. It was there that Wulfila undertook his great project.
He invented a new alphabet for the Gothic language, drawing on Greek, Latin, and runic characters. Then he translated the Bible into Gothic. According to Philostorgius (a 5th-century church historian), Wulfila deliberately omitted the Books of Kings, believing their battle narratives would inflame the Goths’ already excessive enthusiasm for warfare. This detail is debated, but if true, it represents one of history’s more interesting editorial decisions.
The surviving manuscript of Wulfila’s translation, the Codex Argenteus, is a 6th-century copy written in silver and gold ink on purple parchment. It is kept at Uppsala University in Sweden. It is the oldest surviving text in any Germanic language of substantial length.
The consequences of Wulfila’s work were vast. His Arian Christianity spread from the Goths to virtually every Germanic people that encountered the Roman Empire: the Visigoths, Ostrogoths, Vandals, Burgundians, and Lombards all adopted Arian Christianity. When these peoples conquered the Western Roman provinces, the religious divide between their Arian faith and the Nicene Christianity of the Roman population became one of the defining tensions of the early medieval West.
All of this traces back to a single man working in a Balkan city, translating in an alphabet he had invented, transmitting a version of Christianity that the empire was actively trying to suppress.
The Edict of Thessaloniki
The Arian controversy ended, at least officially, with another Balkan moment.
On February 27, 380, Emperor Theodosius I issued the Edict of Thessaloniki (Cunctos populos), making Nicene Trinitarian Christianity the official religion of the Roman Empire. It was issued from Thessaloniki because Theodosius was there, using the city as his military headquarters during the Gothic War (376-382). In the autumn of 379, he had nearly died of an illness and was baptized by the Nicene bishop Ascholius. The edict followed shortly after his recovery.
The language was unusually blunt. All who did not profess the Nicene faith were branded “foolish madmen” (dementes vesanosque) and threatened with divine punishment first, then the punishment of the emperor’s own initiative. This was the first time a Roman emperor had declared a single Christian denomination as the exclusive state religion, with all others criminalized.
The Council of Constantinople in 381 confirmed the edict theologically. It expanded the Nicene Creed to affirm the divinity of the Holy Spirit, condemned six heresies by name, and elevated Constantinople to second rank after Rome in ecclesiastical honor (Canon 3). This last provision infuriated the papacy and would become one of the structural grievances behind the Great Schism.
What happened to the old gods followed gradually. The anti-pagan legislation came in 391-392, not in 380. The pattern in the Balkans was more conversion than outright destruction, though both occurred. At Dodona, one of the most ancient oracle sites in Greece, the sacred oak was cut down around 391-393 and a Christian basilica was built on the site in the 5th century using scavenged materials. At Delphi, the Temple of Apollo was destroyed around 390-391. At Eleusis, the Mysteries were closed by decree in 392 and the sanctuary was physically destroyed by Alaric’s Arian Goths in 396. At Perperikon, the great Thracian sanctuary in the Rhodopes, a church pulpit was added to the summit after the conversion of the Bessi tribe (393-398), while the older altar and processional paths were preserved.
The transition was not always violent. The Thracian Horseman, depicted on over two thousand stone reliefs across the region, was not destroyed. His iconography was absorbed into depictions of Saints George, Demetrius, and Theodore. The rider on horseback who slays a beast is among the most common images in Balkan churches today. The saint’s name is Christian. The pose is Thracian. Sacred springs that had been venerated for centuries became holy water sites blessed by the Church. Dionysian mask traditions survived as kukeri festivals. The mithraea along the Danube frontier were deliberately buried.
What They Built
The archaeological evidence of early Balkan Christianity is concentrated in the 4th through 6th centuries, between the legalization of the faith and the catastrophe that destroyed it.
At Stobi (in modern North Macedonia), a bishop named Budius attended the Council of Nicaea in 325. The Episcopal Basilica dates in its first phase to the mid-4th century, with a monumental expansion under Bishop Philip in the early 5th century. The baptistery is octagonal, surrounded by floor mosaics of peacocks and deer flanking a fountain, referencing Psalm 42: “As a deer pants for flowing streams, so pants my soul for you, O God.”
At Serdica (Sofia), the Council of 343 met in the Episcopal Basilica of Protogenes, on the site where the church of Saint Sofia now stands. Beneath the current church, some fifty tombs dating from the 3rd to the 5th century have been excavated. One bears the inscription “Honorius, servant of God,” the only named early Christian tomb in Bulgaria.
At Philippi, French excavations beginning in 1914 uncovered the forum, theatre, and a series of churches. The most significant is the Basilica of Paul, dated by a mosaic inscription from Bishop Porphyrios to approximately 343-344 AD. This is the earliest epigraphic evidence for the cult of Paul outside Rome. The site became a UNESCO World Heritage Site in 2016.
At Salona (near modern Split, Croatia), the episcopal complex includes a dual basilica and baptistery from the late 4th or early 5th century. The Manastirine cemetery preserves the burial site of Bishop Domnius and other martyrs.
At Heraclea Lyncestis (near Bitola, North Macedonia), the narthex of the great basilica contains a mosaic of over one hundred square meters in approximately twenty colors: grapevines emerging from a fountain, peacocks symbolizing eternal life, deer, fruit trees, and marine animals in surrounding octagonal panels.
And at Caričin Grad, near modern Lebane in Serbia, Emperor Justinian I built an entire city from scratch in the 530s. This was Justiniana Prima, intended to replace Thessaloniki as the ecclesiastical center of Illyricum and to honor Justinian’s birthplace nearby. The city contained ten basilicas. Its episcopal basilica measured sixty-four meters long, with mosaics comparable to Ravenna. Archbishop’s seals found at the site match Procopius’s written description. The entire complex was abandoned around 615, destroyed by the Avars.
The Catastrophe
Everything described above was destroyed.
The Avar and Slavic invasions of the late 6th and early 7th centuries dismantled the Christian infrastructure of the Balkans more thoroughly than anything since the great persecutions. Sirmium, which had hosted five church councils and produced some of the most documented martyrs in Christian history, fell in 582 after a three-year siege. Naissus and Serdica were captured around 615. Justiniana Prima was destroyed in 613 or 615. Salona fell around 614.
By 615, the entire interior of the Balkans was described as “Sklavinia,” settled or controlled by Slavic peoples who were pagan.
Christianity survived in exactly one zone: the Dalmatian coast. The fortified city-states of Ragusa (Dubrovnik), Jader (Zadar), Tragurium (Trogir), Spalatum (Split), and Cattaro (Kotor) held out, their walls facing the sea, their populations a mix of Latin-speaking descendants of the Roman and Illyrian population. Bishops from four of these cities attended the Seventh Ecumenical Council in 787, proving that organized church structures persisted through two centuries of isolation.
For the interior, there is a gap of approximately two hundred years. Almost no written records survive between the early 7th century and the 9th century. Whether any Christianity survived among the Slavic settlers, even in syncretic or degraded form, is an open question. The archaeological evidence for rural continuity exists but is sparse and debated.
The Second Beginning
When Christianity returned to the Balkan interior, it came from two directions at once.
In 863, Emperor Michael III and Patriarch Photius of Constantinople sent two brothers from Thessaloniki, Constantine (later known as Cyril) and Methodius, to Great Moravia. Prince Rostislav had asked for missionaries who could teach in the Slavic language, partly to counter Frankish influence. For the mission, the brothers created the Glagolitic alphabet, the first writing system designed for a Slavic language, and translated the Bible and liturgical texts into what is now called Old Church Slavonic.
The mission to Moravia ended badly. After Methodius died in 885, his disciples were expelled by Frankish bishops who insisted on Latin liturgy. Three of them, Clement, Naum, and Angelarius, made their way south to the First Bulgarian Empire. Boris I of Bulgaria recognized what he had: trained scholars who could build a church infrastructure in a language his people understood.
Boris himself had been baptized in 864 under Byzantine military pressure. But he proved a masterful diplomat, playing Rome against Constantinople to secure an autonomous Bulgarian church. In 866, dissatisfied with Constantinople’s refusal to grant full church independence, he sent emissaries to Pope Nicholas I with a long list of questions about religion, law, and custom. The Pope’s 106 detailed responses (Responsa Nicolai) survive as a remarkable document. By 870, at the Fourth Council of Constantinople, Boris had his autocephalous archbishopric.
Clement was sent to Ohrid, where he founded a literary school that trained approximately 3,500 students over seven years. The Cyrillic alphabet, created in Bulgaria as a simplification of the Glagolitic system using Greek uncial letterforms, was declared the official script in 893. It eventually spread to Serbia, Russia, and the wider Slavic world.
Meanwhile, the Serbs were Christianized during the reign of Knez Mutimir (around 870), under missionaries sent by Emperor Basil I. A bishopric was established after 871. But medieval necropolises show that the process remained incomplete into the 13th century, particularly in rural areas. The baptism of a ruler did not mean the immediate conversion of the population.
The Croats followed a different path. In contact with Latin-speaking Christians on the Dalmatian coast from the moment of their arrival, they were also evangelized by Frankish missionaries from Aquileia and Salzburg. Duke Branimir received papal recognition from Pope John VIII on June 7, 879. Croatia aligned with Rome.
The Fault Line
Croatia went West. Serbia went East. Bosnia, caught between, went neither, producing the medieval Bosnian Church, whose members called themselves simply Krstjani (“Christians”) and whose exact theology is still debated because almost no records survive from the church itself.
The pattern was set by the 9th century and has not fundamentally changed. The line between Catholic and Orthodox Christianity in the Balkans corresponds closely to the line that separated the Roman Empire’s Latin-speaking north from its Greek-speaking south. The philologist Konstantin Jireček identified this boundary through epigraphic evidence in 1911, and it runs, with minor adjustments, through the same territory as the religious divide. Each layer, linguistic, administrative, cultural, religious, reinforced the others.
The Bogomils would emerge in 10th-century Bulgaria, synthesizing older dualist traditions with local discontent against the institutional church. The great heresy trials would come later. The Crusades would deepen the divide. The Ottoman conquest would add another layer entirely.
But the fault line itself was older than all of these. It was visible at Serdica in 343, when the Eastern bishops walked out and the Western bishops stayed. It was deepened in the council halls of Sirmium. It was formalized by geography, language, and imperial administration long before anyone thought to call it a schism.
The first Christians of the Balkans arrived on the Via Egnatia, carrying a message that was supposed to unite. The territory that received that message first became the place where it split. Whether this says something about Christianity, about the Balkans, or about both, is a question the evidence presents but does not answer.
