History of the Catholic Church
Conditions in the Roman Empire facilitated the spread of new ideas. The empire's network of roads and waterways allowed easier travel. Also, the Pax Romana made it safe to travel from one region to another. The government had encouraged inhabitants to learn Greek. Having a  common language allowed ideas to be more easily expressed. Jesus's apostles gained converts in Jewish communities around the Mediterranean Sea. They established over 40 Christian communities by 100. Although most of these were in the Roman Empire, notable Christian communities were also established in Armenia, Iran and along the Indian Malabar Coast. The new religion was most successful in urban areas and it spread first among slaves and people of low social standing, and then among aristocratic women.