Who spread Christianity around the Mediterranean sea?

Answer 1

Christianity spread relatively slowly throughout the Roman Empire until the early fourth century, when Emperor Constantine gave the religion state patronage. The Roman Empire included much of southern and Western Europe, and Christianity also became well established in these areas by the fourth century.

The early Middle Ages, also known as the Dark Ages, began shortly after Christianity finally became the state religion of the empire in the 380s and then worship was banned in pagan temples in 391 CE. So, much of Europe was essentially Christian well before the start of the Medieval Age.

What remained was to Christianise the pagan northern and eastern regions of Europe. There was no real attempt to achieve this by peaceful means, but enslavement and conquest gradually increased the area under Christian control until, finally, all of Europe was Christian.

Answer 2

The Apostle Paul (formerly Saul) brought the message of Christianity to the Mediterranean area.