This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Christianity reaches Sasanian Persia early, carried along trade routes out of Syriac speaking Mesopotamia, with communities attested at Arbela in Adiabene and elsewhere from the late second and third centuries CE. For roughly two centuries the faith grew inside the Sasanian Empire without any single organizing structure, surviving under a government that came to regard it with recurring suspicion.
That suspicion sharpened once Constantine's own conversion gave Rome a Christian emperor, since a Sasanian government now had reason to see its own Christian subjects as a possible pro-Roman fifth column. The worst persecution followed in the fourth century under Shapur II, testing the young Persian church severely.
Toleration came under Yazdegerd I, who permitted open worship from 409, and the shift proved lasting: the Council of Seleucia-Ctesiphon met the following year and organized the empire's scattered Christian communities into a single structure under a Catholicos, the conventional founding date of the Church of the East as an organized body. What this changed for Christianity's spread was decisive: two centuries of loosely connected communities became one recognized church with its own head, planting the institutional base from which the Church of the East would later carry the faith across Central Asia and, within another two centuries, to Tang China itself.