'''Szent Cirill''' ([[Szaloniki|Thesszaloniké]], [] – [[Róma]], []. [[február 14.]]) [[Bizánci Birodalom|bizánci]] filozófus, hittérítő, nyelvtudós, a szláv írás megalkotója, Európa társ-védőszentje, [[Szent Metód]] testvére.
Constantine (who took the name Cyril shortly before his death) studied in Constantinople and later became a professor of philosophy at the university.
The goal of Constantine’s first multilingual, highly educated journey in 851 was to defend Christian doctrines in Christian-Muslim religious debates in the Arab capital. After his return, he continued to teach, and in 858 he went to the monastery for a short time, following his brother, Methodius, who had long chosen a monastic life.
In 860, by two imperial instructions, the two brothers went to the land of the Khazars, where Christian doctrines were spread. During their mission, the remains of a martyr St. Clement were searched in Herson (near Sevastopol, Crimea).
Around 860, on the orders of the Byzantine emperor Michael, he began work on the creation of Slavic writing. Presumably, this alphabet consisted of a total of 43 letters. Thus, the creation of the Cyrillic script, named after him, can be connected to it.
The Ravaslav Moravian prince asked Slavic-speaking monks from Byzantium. The mission was entrusted to Constantine and Methodius, who were well versed in the Slavic language, and their comrades arrived at the court of Rastislav in 863, where, in addition to introducing the Slavic liturgy, a school was established, laying the foundations for Slavic priesthood training. Constantine was also a merit of Slavic writing, the creation and dissemination of the Glagolitic alphabet, and the translation of church books into Slavonic.
Több mint 3 évnyi munkálkodásukat követően 867-ben Rómába mentek, s egyúttal magukkal vitték a Szent Kelemen-ereklyéket is. Konstantin hitvitájában sikeresen megvédte a népnyelv liturgikus használatát azon ellenzőkkel szemben, kik csupán a [[latin nyelv|latin]], [[héber nyelv|héber]] és a [[görög nyelv]]ű liturgiát fogadták el. [[II. Adorján pápa]] engedélyezte a szláv nyelvű liturgiát.