5 As they began their journey through Bulgaria, which had already been converted to Christianity, they let pass no opportunity for increasing the faith. Upon reaching Moravia, they were met by a large crowd who had come with great desire and joy to greet them. Without delay the apostles strove to penetrate their minds with the doctrines of Christianity and to raise their hopes to heavenly things. They did this with so much force and with such energetic zeal that in a very short rime the Moravian people gave themselves to Jesus Christ.
Source: Grande Munus (Vatican.va)