The Church of the East
While the tradition of the Apostolic Church of the East traces its origins back to the apostle Thomas, it is almost certain that the very first Christian congregations emerged within the Jewish communities of the Parthian Empire (247 BCE – 224 CE), which, like the inhabitants of the Roman province of Syria during the first century CE, were Aramaic-speaking.
Judaism had been present in Mesopotamia and across the Tigris at least since the Babylonian exile. At the time of the Parthians, the silk trade with China was under Jewish control. The first to bring Christianity to the East were merchants who traveled the trade routes from the Mediterranean to the Persian Gulf and across Central Asia to China. As Edessa occupied a position where significant trade routes intersected, and Antioch on the Mediterranean was the most influential metropolis of the Roman province of Syria, the Gospel traveled a route from Jerusalem through Antioch and Edessa to Mesopotamia.
By 823, the Church of the East, based in Mesopotamia, had a missionary presence that encompassed India, China, Turkestan, Yemen, and around the Caspian Sea. Traveling the same paths as merchants and mariners, they claimed tens of millions of adherents in 230 dioceses with twenty-seven metropolitans.