Edessa gave Christianity a third language. Syriac, the literary form of the Aramaic spoken there, became the medium of a body of theology, poetry, biblical translation and later of science and philosophy, and it carried the faith east into Persia, Central Asia, India and China. The Peshitta, the standard Syriac Bible, took shape in this environment, as did the Diatessaron, a single narrative woven from the four gospels that was read in Syriac churches for centuries before being suppressed in favour of the separated gospels.
Ephrem moved to Edessa in 363, when Nisibis was ceded to Persia, and spent his last decade there. He wrote theology in verse, in hymns built on repeated images rather than on definitions, and he is recorded as having trained choirs of women to sing them, which in the fourth century was both a pastoral method and a polemical one, since the followers of Bardaisan had used hymns effectively before him.
The school of Edessa taught in the Antiochene manner and translated Theodore of Mopsuestia into Syriac. When that tradition fell under suspicion after the condemnation of Nestorius, the emperor closed the school in 489, and its teachers crossed the frontier to Nisibis in Persian territory, where they refounded it. That relocation is why the Church of the East, outside Roman control, became the custodian of Antiochene exegesis and the missionary church of Asia. The modern city, Sanliurfa, venerates a cave as the birthplace of Abraham and draws pilgrims to the pools of fish beside it.