He enjoyed a good education and became acquainted with Greek culture. Extensive travels led him through different countries and showed him the nature of Greek education, art, and science. He himself states that he studied the pagan religions.

Finally he came to Rome, where he seems to have remained for some time. Here he seems to have come for the first time in touch with Christianity. According to his own representation, it was primarily his abhorrence of the heathen cults that led him to spend thought on religious problems. By the Old Testament, he says, he was convinced of the unreasonableness of paganism. He adopted the Christian religion and became the pupil of Justin Martyr. It was the period when Christian philosophers competed with Greek sophists, and like Justin, he opened a Christian school in Rome. It is not known how long he labored in Rome with out being disturbed.

The later life of Tatian is to some extent obscure. Since the "Address to the Greeks" was written probably in Greece, it may be inferred that he tarried in that country for some time. Epiphanius relates that Tatian first established a school in Mesopotamia, the influence of which extended to Antioch in Syria, and was felt in Cilicia and especially in Pisidia, but these statements can not be verified.

The later activity of Tatian is attested by the history of the Diatessaron (see below).

Irenaeus remarks (Haer., I., xxvlii. 1, ANF, i. 353) that Tatian after the death of Justin separated from the Church and taught Encratitic heresy, also a doctrine of eons related to that of Valentine. Such statements are to be received with caution; for the Western churcht regarded as heretical much which the Eastern judged orthodox.

The ascetic character which Syriac Christianity bore as late as the time of Aphraates was not impressed upon it by Tatian, but has roots that reach deeper.

Tatian was the first to give the Syriac congregations the Gospel in their own language. The Syrian church possessed and used the Gospel from the very beginning until the time of Rabbula[?] only in the form of the Diatessaron; it is probable, therefore, that Tatian not only brought the Diatessaron into Syria, but also developed there a successful missionary activity in the last quarter of the second century. A later age did not realize that the Syrian ascetic tendencies had been transmitted from Semitic primitive Christianity, hence it regarded Tatian as a sectarian, the head of the Encratites.

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.

Writings

His "Address to the Greeks" tries to prove the worthlessness of paganism, and the reasonableness and high antiquity of Christianity. It is not characterized by logical consecutiveness, but is discursive in its outlines. The carelessness in style is intimately connected with his contempt of everything Greek. No educated Christian has more consistently separated from paganism; but by overshooting the mark, his scolding and blustering philippic lost its effectiveness because it lacks justice. But Tatian was praised for his discussions of the antiquity of Moses and of Jewish legislation, and it was because of this chronological section that the "Address" was not generally condemned.

His other major work was the Diatessaron, a "harmony" or synthesis of the four New Testament Gospels into a combined narrative of the life of Jesus Christ. Also known as the "Evangelion da Mehallete" (the Gospel of the mixed), it was practically the only gospel text used in Syria during the third and fourth centuries.

In the fifth century the Diatesseron was replaced in the Syrian churches by the four original Gospels. Rabbula[?], Bishop of Edessa (411-435), ordered the priests and deacons to see that every church should have a copy of the separate Gospels (Evangelion da Mepharreshe), and Theodoret, Bishop of Cyrus (423-457), removed more than two hundred copies of the Diatesseron from the churches in his diocese.

Two revisions of the Diatesseron are available: one in Latin preserved in the "Codex Fuldensis" of the Gospels dating from about A.D. 545, the other in an Arabic version found in two manuscripts of a later date.

In a lost writing, entitled On Perfection according to the Doctrine of the Savior, Tatian designates matrimony as a symbol of the tying of the flesh to the perishable world and ascribed the "invention" of matrimony to the devil. He distinguishes between the old and the new man; the old man is the law, the new man the Gospel.

Other (lost) writings of Tatian are a work written before the "Address to the Greeks" and treating the nature of man as contrasted with the nature of the animals, and a Problematon biblion, which aimed to present a compilation of obscure Scripture sayings.

Theology

The starting-point of Tatian's theology is a strict monotheism which becomes the source of the moral life. Originally the human soul possessed faith in one God, but lost it with the fall. In consequence man sank under the rule of demons into the abominable error of polytheism. By monotheistic faith the soul is delivered from the material world and from demonic rule and is united with God. God is spirit (pneuma), but not the physical or stoical pneuma; he was alone before the creation, but he had within himself potentially the whole creation.

The means of creation was the dynamis logike ("power expressed in words"). At first there proceeded from God the Logos who, generated in the beginning, was to produce the world by creating matter from which the whole creation sprang. Creation is penetrated by the pneuma hylikon, "world spirit," which is common to angels, stars, men, animals, and plants. This world spirit is lower than the divine pneuma, and becomes in man the psyche or "soul," so that on the material side and in his soul man does not differ essentially from the animals; though at the same time he is called to a peculiar union with the divine spirit, which raises him above the animals. This spirit is the image of God in man, and to it man's immortality is due.

The first-born of the spirits fell and caused others to fall, and thus the demons originated. The fall of the spirits was brought about through their desire to separate man from God, in order that he might serve not God but them. Man, however, was implicated in this fall, lost his blessed abode and his soul was deserted by the divine spirit, and sank into the material sphere, in which only a faint reminiscence of God remained alive.

As by freedom man fell, so by freedom he may turn again to God. The Spirit unites with the souls of those who walk uprightly; through the prophets he reminds men of their lost likeness to God. Although Tatian does not mention the name of Jesus, his doctrine of redemption culminates in his Christology.