Tatian the Assyrian[1][2][3][4] (/ˈteɪʃən, -iən/; Latin: Tatianus; Greek: Τατιανός; Syriac: ܛܸܛܝܢܐ; c. 120 – c. 180 AD) was an Assyrian early Christian writer and theologian of the 2nd century.
Tatian's most influential work is the Diatessaron, a Biblical paraphrase, or "harmony", of the four gospels that became the standard text of the four gospels in the Syriac-speaking churches until the 5th-century, after which it gave way to the four separate gospels in the Peshitta version.
Concerning the date and place of his birth, little is known beyond what Tatian tells about himself in his Oratio ad Graecos, chap. xlii (Ante-Nicene Fathers, ii. 81–82): that he was born in "the land of the Assyrians"; scholarly consensus is that he died c. 185 AD, perhaps in Assyria.
He traveled to Rome, where he first encountered Christianity. During his prolonged stay in Rome, according to his own representation, his abhorrence of the pagan cults sparked deep reflections on religious problems. Through the Old Testament, he wrote, he grew convinced of the unreasonableness of paganism. He adopted the Christian religion and became the pupil of Justin Martyr. During this period Christian philosophers competed with Greek sophists. Like Justin, Tatian opened a Christian school in Rome. It is not known how long he labored in Rome without being disturbed.
Knowledge of Tatian's life following the death of Justin in 165 AD is to some extent obscure. Irenaeus remarks (Haer., I., xxvlii. 1, Ante-Nicene Fathers, i. 353) that after the death of Justin, he was expelled from the church for his Encratitic (ascetic) views. (Eusebius claims he founded the Encratitic sect), as well as for being a follower of the gnostic leader Valentinius. It is clear that Tatian left Rome, perhaps to reside for a while in either Greece or Alexandria, where he may have taught Clement of Alexandria.[6] Epiphanius relates that Tatian established a school in Mesopotamia, the influence of which extended to Antioch in Syria, and was felt in Cilicia and especially in Pisidia.
The early development of the Syrian church furnishes a commentary on the attitude of Tatian in practical life. Thus for Aphraates baptism conditions the taking of a vow in which the catechumen promises celibacy. This shows how firmly the views of Tatian were established in Syria, and it supports the supposition that Tatian was the missionary of the countries around the Euphrates.