Christianity spread to the
Balkans beginning in the 1st century.
Florus and Laurus are venerated as Christian martyrs of the 2nd century; they were murdered along with 300 Christians in
Constantine the Great (306–337), born in
Niš, was the first Christian
Roman Emperor. Several bishops seated in what is today Serbia participated in the
First Council of Nicaea (325), such as
Ursacius of Singidunum. In 380, Eastern Roman Emperor
Theodosius decreed that his subjects would be Christians according to the Council of Nicea formula. Greek was used in the Byzantine church, while the Roman church used Latin. With the definite split in 395, the line in Europe ran south along the
Drina river. Tim Judah says that the Roman split resulted in that Serbs are Orthodox and the Croats Catholic. Among old Christian heritage is the
Archbishopric of Justiniana Prima, established in 535, which had jurisdiction over the whole of present-day Serbia. However, the Archbishopric did not last, as the Slavs and
Avars destroyed the region sometime after 602, when the last mention is made of it. In 731
Leo III attached
Southern Italy (Sicily and Calabria) to
Patriarch Anastasius of Constantinople, transferring the papal authority to the Eastern Church.
Christianization of Serbs
The history of the early medieval
Serbian Principality is recorded in the work
De Administrando Imperio (DAI), compiled by the Byzantine Emperor
Constantine VII Porphyrogenitus (r. 913–959). The DAI drew information on the Serbs from, among others, a Serbian source. The Serbs were said to have received the protection of Emperor
Heraclius (r. 610–641), and Porphyrogenitus stressed that the Serbs had always been under Imperial rule. His account on the first Christianization of the Serbs can be dated to 632–638; this might have been Porphyrogenitus' construction, or may have really taken place, encompassing a limited group of chiefs and then very poorly received by the wider layers of the tribe. The establishment of Christianity as state religion dates to the time of Prince
Mutimir (r. 851–891) and
Basil I (r. 867–886); Porphyrogenitus attests that Croats and Serbs sent delegates asking for baptism, thus Basil "baptized all of them that were unbaptized of the aforesaid nations". The
Christianization was due partly to Byzantine and subsequent Bulgarian influence. At least during the rule of
Kocel (861–874) in Pannonia, communications between Serbia and Great Moravia, where
Methodius was active, must have been possible. This fact, the pope was presumably aware of, when planning Methodius' diocese as well as that of the Dalmatian coast, which was in Byzantine hands as far north as
Split. There is a possibility that some
Cyrillomethodian pupils reached Serbia in the 870s, perhaps even sent by Methodius himself. Serbia was accounted Christian as of about 870.
first Serbian bishopric was founded at
Ras, near modern
Novi Pazar on the
Ibar river. According to Vlasto, the initial affiliation is uncertain; it may have been under the subordination of either Split or Durazzo, both then Byzantine. The early
Ras church can be dated to the 9th–10th century, with the rotunda plan characteristic of first court chapels. The bishopric was established shortly after 871, during the rule of Mutimir, and was part of the general plan of establishing bishoprics in the Slav lands of the empire, confirmed by the
Council of Constantinople in 879–880. The names of Serbian rulers through
Mutimir (r. 851–891) are
Slavic dithematic names, per the Old Slavic tradition. With Christianization in the 9th century, Christian names appear.
 The next generations of Serbian royalty had Christian names (Petar, Stefan, Pavle, Zaharije, etc.), evident of strong Byzantine missions in the 870s.
Petar Gojniković (r. 892–917) was evidently a Christian prince, and Christianity presumably was spreading in his time; also since Serbia bordered Bulgaria, Christian influences and perhaps missionaries came from there, increasing during the twenty-year peace. The Bulgarian annexation of Serbia in 924 was important for the future direction of the Serbian church, and by then, at latest, Serbia must have received the Cyrillic alphabet and Slavic religious text, already familiar but perhaps not yet preferred to Greek.
Archbishopric of Ohrid (1018–1219)
In 1018–19, the
Archbishopric of Ohrid was established after the Byzantines conquered
Greek replaced Slavic as the liturgical language. Serbia was ecclesiastically administered into several bishoprics: the
bishopric of Ras, mentioned in the first charter of Basil II (r. 976–1025), became part of the Ohrid archbishopric and encompassed the areas of southern Serbia, by the rivers
Raška, Ibar and Lim, evident in the second charter of Basil II. In the chrysobulls of Basil II dated to 1020, the Ras bishopric is mentioned as serving the whole of Serbia, with the seat at the
Church of the Holy Apostles Peter and Paul, Ras. Among the first bishops were Leontius (fl. 1123-1126), Cyril (fl. 1141–1143), Euthemius (fl. 1170) and Kalinik (fl. 1196). It later joined the autocephalous
Archbishopric of Žiča in 1219, at the time of Saint Sava.
The 10th- or 11th-century Gospel Book
Codex Marianus, written in
Old Church Slavonic in the
Glagolithic script, is one of the oldest known Slavic manuscripts and was partly written in the Serbian redaction of
Old Church Slavonic. Other early manuscripts include 11th-century
Grškovićev odlomak Apostola and