The apostles of Jesus Christ help spread what was later called Christianity. At first people such as the Romans and others considered the apostles and what they taught to be a Jewish sect. By the end of the 1st century it was clear that it was not a sect, but a different religion.
Kings and Monasteries helped to spread Christianity.
Paul
Paul of Tarsus, who was previously known as Saul spread Christianity as the first Christian missionary, or person who spreads their belief to non-believers. He travelled across the Roman Empire, sending Christian messages to gentiles and non-Jewish communities as well as to Jews. This allowed more people to follow the faith. He preached about Christianity in new areas where no one had preached before, and established Christianity there.
clovis helped spread christianity by making it the only legal religion
Saul of Taurus, who converted on the road to Damascus, and became St. Paul. He was arrested by the Romans and was executed (by beheading) in Rome.
Kings and Monasteries helped to spread Christianity.
Charlemagne helped spread Christianity throughout the Frankish Empire and the lands he conquered. He spread Christianity through both peaceful conversion efforts and military conquests.
the bible
They built the Vatican.
medieval missionaries
Trade.
As Christianity spread it faced many oppositions. Some of the Christian that helped in spreading the gospel were persecuted, jailed and tortured.