Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 1. Spread of Christianity.”
§6. Means of Propagation.
Schaff notes that there is little information about missionaries until the start of the Medieval period. However, by the early fourth century the Roman empire was at least nominally Christian (Schaff 2014, Loc. 12380). He sees this as a natural growth, occurring simply because of the commitment of individual Christians and congregations. Along with word of mouth, the Scriptures were widely trnslated and distributed (Schaff 2014, Loc. 12399).
§7. Extent of Christianity in the Roman Empire.
Schaff quotes Justin Martyr, Tertullian, and Origen to indicate that Christianity was known in one way or another by people all over the Roman empire (Schaff 2014, Loc. 12408). Schaff observes that “the fact that the Christians were a closely united body, fresh, vigorous, hopeful, and daily increasing, while the heathen were for the most part a loose aggregation, daily diminishing, made the true prospective strength of the church much greater” (Schaff 2014, Loc. 12418). The unified witness of Christ also led to other types of unity and thus economic and political advances in communities where there were large concentrations of Christians.
§8. Christianity in Asia.
During the first three centuries of the Christian period, Christianity spread broadly through Asia Minor. By the early second century much of what we consider the Middle East had an established church. The third century saw a spread into Armenia, Arabia, and possibly India (Schaff 2014, Loc. 12437). By 325 Constantinople became a center of Christianity. Schaff notes that the forceful spread of Islam hindered the growth and brought many Christians into bondage, but that there remains hope that the Christian message will again become clear in the region.
§9. Christianity in Egypt.
Egypt had long been a center of Jewish learning. In the apostolic period, there is evidence for the spread of Christianity into Egypt as well (Schaff 2014, Loc. 12446). The evangelist Mark is thought to have founded the church in Alexandria. There were bishops and theological schools there from the early Christian period (Schaff 2014, Loc. 12456). Again, Schaff notes that Islam has disrupted Christianity since 640, but that there has been a continued Christian presence.
§10. Christianity in North Africa.
The North African area around Carthage was largely a migrant population, having come from the Semitic peoples. Schaff notes a Romanization of the region. Due to the Roman dominance, the Phoenecians, who spread throughout the Mediterranean and especially around Carthage, became part of Latin Christianity (Schaff 2014, Loc. 12474). This, again, was interrupted by Islam, though it had suffered under the Vandals as early as 439. Before the Islamic invasions a broad swath of northern Africa was Christian, with duly established bishops in many areas (Schaff 2014, Loc. 12491). Augustine, one of the leaders of early fifth century Christian thought, was from this area.
§11. Christianity in Europe.
Schaff traces Christianity as tending to move from East to West, gaining its most important center in Rome by the mid third century. He estimates about 50-60,000 Christians in Rome itself in the mid third century (Schaff 2014, Loc. 12511). Christianity spread throughout modern day France by the end of the second century. Schaff notes Christianity in Spain during the third century (Schaff 2014, Loc. 12520). Irenaeus and Tertullian assert that there was a Christian witness in Germany and Britain as early as the second century. This was certainly an influential region in world Christianity from an early period (Schaff 2014, Loc. 12529).