Syrian Christianity flourished in three ancient cultural centres, Edessa in the east of Upper Euphrates, Ediabene in the east of Upper Tigris, and Seleucia-Ctesiphon on the Lower Tigris. These centres adopted Aramaic as the main language during the neo-Assyrian period, and by the fifth century B.C., this language became the lingua franca of the entire Near East. Aramaic culture, heavily influenced by the ancient cultures of Assyria and Babylonia, marked these regions before they fell under the cultural hegemony of the Greeks, especially in the case of Edessa. Nevertheless, when the kingdom of Edessa ,Abgar, officially adopted Christianity by the third century, its own Aramaic dialect, Syriac, became the language of the Christians in both Syria and Mesopotamia. By sifting through sources remarking on Abgar, especially the Doctrine of Addai, we learn about the earliest history of Syrian Christianity and religious syncretism with earlier paganism. Furthermore the Place of Edessa (Urhai) as a semi-autonomous city-state and as an ethnic crossroads plays an important role to this end as well, as it accommodates Christian development, In spite of persecution from the governments of Iran and Rome and the religious leaders, Christianity Church flourished during this time in Asia up to the late Middle Age, This was a historical research, in which data collected from written sources was analyzed using a descriptive-analytic approach.