Tatian, a Syrian, was born around 120 CE in Assyria and died around 173 CE.

He left eastern Syria and became a traveling scholar. He was trained in various schools of Greek philosophy, especially Stoicism, before reading the Septuagint, which led him to become a Christian about 150 CE. He traveled to Rome and became a student of Justin. After Justin was martyred, in 163 CE, Tatian became severe about several subjects, rejecting all marriage, eating no meat, or drinking any alcohol, which included the Eucharist. As a result of these beliefs and being outspoken about them, the Church of Rome declared him a heretic and excommunicated him from the Church, about 172 CE, according to Irenaeus. Tatian returned to Syria and a sect developed called the Encratites ("those who exercise self-control").

Tatian is known for his compiling of the books of MaththiYahu, Mark, Luke and Yahuchanan, called the Diatessaron, the harmony of the four. It was based on the book of Yahuchanan. His work was received and widely used in the churches of the East and the West. Later, in 436 CE, Rabbula the Bishop of Edessa began to make reforms in the Church. Because he considered Tatian a heretic, Rabbula felt that the Diatessaron could not be used. He instructed his priests to only use the separated books of MaththiYahu, Mark, Luke and Yahuchanan. Rabbula wrote the Aramaic Peshitta between 411-435 and this became the text that was used in the churches of the east.