The early Christian Church expanded through the preaching of people traveling along the roads of the Roman Empire. This characteristics is most visible when comparing the details of such an expansion with the map of major Roman roads. After a time of persecution throught the Roman Empire, it finally became the official religion of the Empire in 313 AC, under the reign of Constantine (who also move the Empire capital to a new city, Constantinople).
The following map shows the expansion of the Christian faith around the Mediterranean Sea. Evidences of Christian presence have also been found as far as India (from the 1th century), Sri Lanka (from the 1th century) and China (from the 6th century).