Edessa, a small kingdom lying at the eastern edge of the Roman Empire, became a center for eastern, Aramaic Christianity. It was eventually absorbed into the Roman Empire and later into the Persian empire.
After Jesus was risen from the abode of the dead and was received into heaven, Thomas the apostle . . . by an impulse from God, sent Thaddaeus . . . to Edessa to be a preacher and proclaimer of the teaching of Christ. And the promise of Christ was fulfilled through him. You have in writing the evidence of these things, which are taken from the book of records that was at Edessa. For at that time, the kingdom was still standing. Eusebius (c. 315, E), 8.651