This would be from the Assyrian Church - the ancient church of the east that was and IS headquartered in Ctesiphon, the one-time capital of the Sassanid Persian empire. Ctesiphon is near Babylon and Baghdad.
The Ancient Church of the east stretched from Ctesiphon through the Persian gulf to India and to Mongolia - the wife of Genghis Khan was born into a Christian family belonging to the church of the east.
In the 8th century, fully one third of all Christians belonged to the Ancient Church of the east, lead by the Catholicos in Ctesiphon
Under Sasanian rule, the population of Ctesiphon was heavily mixed: it included Arameans, Persians, Greeks and Assyrians. Several religions were also practiced in the metropolis, which included Christianity, Judaism and Zoroastrianism.