The characters in this alphabet were thirty-eight in number.

Kyrill, with the aid of his brother Methody, then proceeded to make his translations of the Church Service books.

The Bulgarians became Christians in the year 861, and these books were adopted by them.

But the greatest activity of the brothers was during the four and a half years beginning with the year 862, when they translated the holy Scriptures, taught the Slavonians their new system of reading and writing, and struggled with heathendom and with the German priests of the Roman Church.

These German ecclesiastics are said to have sent petition after petition to Rome, to Pope Nicholas I., demonstrating that the Word of God ought to be preached in three tongues only--Hebrew, Greek, and Latin--"because the inscription on the Cross had been written by Pilate in those tongues only." Pope Nicholas summoned the brothers to Rome; but Pope Adrian II., who was reigning in his stead when they arrived there, received them cordially, granted them permission to continue their preaching and divine services in the Slavonic language, and even consecrated Methody bishop of Pannonia; after which Methody returned to Moravia, but Kyrill, exhausted by his labors, withdrew to a monastery near Rome, and died there in 869.
The language into which Kyrill and Methody translated was probably the vernacular of the Slavonian tribes dwelling between the Balkans and the Danube.