The history of Christianity in Hungary started in the Roman province of Pannonia, centuries before the arrival of the Magyars, or Hungarians.
Roman Pannonia
Celtic, Illyrian, Iranian and Dacian tribes inhabited the lands now forming Hungary in classical antiquity. The Romans started the conquest of the tribes of Transdanubiathe western region of present-day Hungaryin 35BC. The region was incorporated in the Roman province of Pannonia in 9AD, and split into two new provinces, Pannonia Prima and Valeria, in the 290s. The Pannonian natives' religion is poorly documented but the Romans erected shrines to their gods. A Christian presence can certainly be documented from the 2ndcentury. A decorated casket-mount depicting the marriage at Cana and other scenes from the Bible was unearthed in the , or civil settlement, at the fort of Intercisa (now Dunaújváros). The first Christians were immigrants, particularly from Syria, Italy and Greece. Most of them had Greek names. One of the earliest tombstones with a Christian inscription"Live in God"was erected for Aurelius Iodorus, "a Greek citizen from Laodicea area", and his two children in the , or city, of Savaria (now Szombathely). No Christian churches dated before the 4thcentury have been unearthed, implying that Christian liturgy was celebrated in private homes.
The Diocletianic Persecution did not severely affect the Transdanubian Christian communities. No local martyrs are known, although Bishop Quirinus of Sescia (now Sisak in Croatia) was publicly executed in Savaria in 303. Shortly after the Roman emperor Constantine the Great () legalised Christianity in 313, Christian cemeteries, separated from the pagans' necropolises, were developing near the Roman towns and fortresses. The use of fibulae decorated with Christian symbols such as crosses or "Chi Rho"-monograms spread, although they do not necessarily evidence their owners' genuine Christian faith because Christianity became a state religion during this period. Although none of the towns of Pannonia Prima and Valeria are documented as episcopal sees, the historian András Mócsy emphasises that bishoprics must have existed in the provincial capitals, Sopianae and Savaria. Ambrose (d. 397), Archbishop of Milan, writes that Arianisma doctrine condemned as heresy at the First Council of Nicaeawas spreading in Pannonia Valeria in the 4thcentury. The writer Sulpicius Severus (d. 425) adds that Martin of Tours (d. 397) who had been born to pagan parents in Savaria in 316 or 317 was expelled from the city by Arian clergy after he converted his mother to Nicaean Christianity.
Early Middle Ages
Migration period
The Huns crossed the Volga River from the east and forced large groups of Alans and Goths to abandon their homelands in the Pontic steppes. Hun, Alan and Goth troops pillaged Pannonia for the first time in the winter of 379–380. The Romans allowed the Marcomannic queen Fritigil and her people to settle in Pannonia Prima after she converted to Christianity and convinced her husband to surrender to imperial authority around 396. In the early , the westward migration of peoples resumed, and Pannonia was invaded by Goths and Vandals. The violent incursions forced parts of the Romanized population to flee from Pannonia. Christians who fled from the town of Scarbantia (now Sopron) took Bishop Quirinus's relics from Savaria to Rome around 408. The Huns' center of power was transferred to the lowlands along the Middle Danube in the 420s, but their empire collapsed due to a rebellion by the subject peoples in 454. Thereafter, Germanic peoples were fighting for hegemony along the Middle Danube. By the early , the Gepids became the dominant power in the lands to the east of the river Tisza, and another Germanic group, the Lombards seized Pannonia. Native Christian groups survived the calamities. Anthony the Hermit who was born to an aristocratic family in Valeria left the province only after his parents' death sometime in the . In the next century, Martin (d. 580), who would become archbishop of Braga (in present-day Portugal), was born in Pannonia.
The Gepids' conversion to Arian Christianity started in the second half of the 4thcentury. The 6th-century Gothic historian Jordanes attributes their conversion to the efforts of the Arian Roman emperor Valens (). Archaeological finds proving the survival of Germanic paganism among the Gepids abound, but their leaders were buried with reliquiaries, indicating the veneration of saints. The Lombards came into contact with Arian missionaries in the 490s, but their pagan funerary rites survived. Arianism became their dominant religion in the 560s, which separated them from the natives who adhered to mainstream Christianity. Nicetius (d. 566), Bishop of Trier, addressed a letter to Chlothsind (d. 568), the Frankish wife of the Lombard king Alboin () in the winter of 565–566, urging her to convert her Arian husband. The Avars—a powerful coalition of steppe peoples—invaded the Gepids' land and forced them into submission in 567. A year later, the Lombards voluntarily left Pannonia for Italy, accompanied by other groups such as Gepids and Romanized natives as well. The Avars were pagans who placed large quantities of grave goods in the graves, and buried their warriors together with their horse or its parts. The 6th-century Byzantine historian Menander Protector writes that the Avars swore by "God in heavens", whom the historian Walter Pohl associates with the Turkic supreme god Tengri. The Avars encouraged the Slavs to settle on the fringes of their empire, contributing to the Slavs' expansion in Central Europe.
A Christian community, the bearers of the Keszthely culture, flourished in the region of a former Roman fortress at Keszthely in the Avar Khaganate. The local basilica with three apses was used and possibly reconstructed in the second half of the 6thcentury. The community leaders were buried in the basilica or in the nearby cemetery. A wealthy woman buried in the cemetery wore a silver garment pin with the inscription BONOSA, tentatively identified as her name. The origin of the community is uncertain, with some scholars regarding them as the descendants of the local Romanized population, others identifying them as Byzantine prisoners of war, or a mixed population of local Christians and immigrants from various lands. Although the Keszthely fortress and the basilica were destroyed, most probably during an Avar civil war around 630, the community survived, developing new cemeteries in the region, but their distinctive culture quickly disappeared.
Columbanus (d. 615) was the first known missionary to be contemplating proselytizing among the Avars and the Slavs around 610. He quickly abandoned the idea after realizing that "progress in faith for this people was not ready to hand", according to his biographer Jonas of Bobbio (d. after 659). Around 700, Bishop Emmeram of Regensburg (d. 652) was planning to visit the Avars, but Bavarian officials dissuaded him from crossing the border. The Avars supported the opponents of the Frankish king Charlemagne (), provoking a Frankish military campaign in 791. A civil war broke out in the khaganate, and a high-ranking Avar dignitary, the , converted to Christianity in the hope of Frankish support. In 796, Charlemagne's son, Pepin the Hunchback (d. 811) launched a successful military campaign against the Avars. The bishops who accompanied him held a synod on the Danube in 796, presided over by Patriarch Paulinus II of Aquileia (d. 802/804). They discussed the methods of the Avars' conversion, describing them as an illiterate and irrational people, and concluding that they could not be converted by force. The missionary territories were distributed between the sees of Aquilea and Salzburg along the river Dráva, with the lands to the north of the river coming under the jurisdiction of Salzburg.
Slavic tribes began raiding the Avar territories, forcing one of the Avar leaders, the Theodore, who was Christian, to seek assistance from the Franks. He and his people were settled in the lands between Savaria and Carnuntum. The Avar also converted to Christianity near Carnuntum on 21 September 805, receiving the name Abraham. A Byzantine list of bishoprics, compiled probably between 806 and 815, mentions the Avars among the Christian peoples under the jurisdiction of the papacy. The Avars' power quickly disintegrated and no Avar dignitaries were mentioned after 821. Cemeteries testify to the survival of the traditional Avar burial rites in southwest Transdanubia until around the middle of the .
Carolingian Age
Transdanubia was integrated in the administrative system of the Carolingian Empire between 796 and 828. The see of Salzburg ceded the lands to the west of the river Rába to the bishopric of Passau. Both prelates appointed evangelising bishops to direct proselytising missions in the region, but few archaeological finds indicate the existence of Christian communities during the first half of the . A pagan aristocrat, Pribina (d. 861), whom the Moravians had expelled from his lands across the Danube, sought refuge in the Carolingian Empire in 833. He was baptised on the order of King Louis the German () who also granted him estates on the river Zala. Pribina built a fortress, Mosapurc, in the swamps near Lake Balaton (at present-day Zalavár), and settled Slavic, Bavarian and Swabian colonists in his estates. A baptistery existed in Mosapurc already in the late 840s; Liupramm (d. 859), Archbishop of Salzburg, consecrated a church in the town on 24January 850. The Saxon wandering priest, Gottschalk (d. 868), visited Pannonia in early 848, shortly before his teaching about predestination was condemned as heresy at a synod in Mainz. A three-aisled basilica, dedicated to St Adrian (d. 306), was built in Mosapurc around 855.
Pribina died fighting against the Moravians, and his son, Kocel (d. 874), succeeded him. Adalwin (d. 873), Archbishop of Salzburg, did not appoint evangelising bishops to Pannonia from around 863, likely as a consequence of a conflict with the last of the bishops, Osbald who twice approached directly the papacy for advice. Kocel met the Byzantine missionary brothers, Constantine (d. 869) and Methodius (d. 885), during their journey from Moravia to Rome in 867. Constantinethe future St Cyrilhad constructed a special alphabet for the Slavic languages and developed a Slavic liturgy. Kocel learnt the new script and entrusted the brothers with the education of . In Rome, Pope Hadrian II (d. 872) approved the Slavic liturgy, and Methodius returned to Mosapurc in 869.
Kocel persuaded the Pope to appoint Methodius as bishop of the "see of St Andronicus" in Pannonia, which limited the jurisdiction of the archbishopric of Salzburg and the bishopric of Passau. Around 870, an unidentified cleric compiled a historical work, the Conversion of the Bavarians and the Carantanians to defend the interests of the Salzburg see. When Methodius left Pannonia for Moravia in early 870, Bishop Ermanrich of Passau (d. 874) arrested him, and a synod of the Bavarian prelates ordered Methodius' imprisonment for his interference in church affairs in Transdanubia. After Methodius's arrest, his pupils had to flee from Kocel's domains. Pope John VIII (d. 882) achieved Methodius' release early in 873, but Methodius could not return to Mosapurc because Kocel feared of the Bavarian bishops' revenge. After Kocel died around 875, Arnulf of Carinthia (d. 899) seized his domains. During his rule, the St Adrian Basilica was rebuilt in Mosapurc.