Tatian of Adiabene, or Tatian the Syrian or Tatian the Assyrian, (; ; ; ; c. 120 – c. 180 AD) was an Assyrian 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. Life 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. AD 185, perhaps in Adiabene. He travelled 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. Knowledge of Tatian's life following the death of Justin in AD 165 is to some extent obscure. Irenaeus remarks (Haer., I., xxviii. 1, Ante-Nicene Fathers, i. 353) that after the death of Justin, he was expelled from the church for his Encratitic (ascetic) views, as well as for being a follower of the gnostic leader Valentinius. Eusebius refers to a belief that Tatian had founded the Encratitic sect. 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. 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 Aphrahat 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. Writings His Oratio ad Graecos (Address to the Greeks) condemns paganism as