Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
a notable Christian writer of the 2nd century, was a native of Assyria, though Clemens Alexandrinus and later fathers term him a Syrian. He had mastered the Graeco-Romaun culture of his day, largely through extended travels; and his reading was very wide, no fewer than ninety-three classic authors being referred to in his works. In the course of his wanderings as a strolling rhetorician he came to Rome, at that time the great center for all intellectual interests and tendencies, and there turned his attention to Christianity. To justify this action he wrote his Λόγος Πρὸς ῾Ελληνας , a work in which he confesses himself a convert to the barbarian philosophy of the despised sect, and invites his contemporaries to examine it, that they too might observe the astonishing contrasts it presents, with its simplicity and its clearness, to the darkness of the heathenism of that and every other age. At Rome Tatian was associated with Justin, perhaps as a pupil; but he soon became himself a teacher of Christianity. His attitude was apologetic, and necessarily involved the most marked antagonism to paganism. Stern and even harsh in his morality, he could recognize no truth in heathen philosophy, and feel no sympathy, even though but of a scientific or vesthetical nature, with heathen life and culture. To him, as to his contemporary Christians, the belief in One God was of the highest moral significance.
The loss of this faith, he taught, had exposed the soul of man to the rule of the dark powers of material nature, the daemons with whom polytheistic views originate. Its recovery delivers from servitude to the wandering daemons (the planets) upon which astrological fate is based. In opposition to the materialistic pantheism of the Stoics, Tatian defended the supermundane spirituality of the one God, the Creator and First Cause of all things, in whom, as the Great Source of being, all things, including matter, potentially existed at the first. At the beginning the Logos sprang into being as the first-born work of the-Father, that he might produce the world, himself creating the material. The created universe is everywhere pervaded by the spirit of material life, which is inferior to the Divine Spirit being in man the soul, which is indissolubly connected with the body, and in the world the world-soul ( Πνεῦμα Ὑλικόν ). Human nature in its pure state is, however, privileged to a substantial and intimate union ( Συζυγία ) with the perfect nature, the Spirit of God himself. This throws a significant light upon Tatian's conception of the Trinity.
He teaches that as the Father is (in his essence) Spirit, so the Logos proceeding from the Father is Spirit; and the latter, that he might imitate the Father, has made man in the image of immortality, to the end that man might have part in God and attain to immortality. The Spirit thus became the life-companion of the soul. In this way God himself lives in man by his ministering Spirit, by which is to be understood simply the hypostatized efficiency of the Logos. The fall involved the removal of the Divine Spirit from the soul, and plunged the latter deeper into the condition of the merely hylic, so that but faint sparks of the Spirit and dim longings after God remain. It is possible, however, for-the soul to turn away from evil and towards God in the exercise of its freedom-how, Tatian does not clearly state. The fame which Tatian acquired through his apology, from which the foregoing sketch is principally taken, was lost in consequence of his perversion to Gnosticism. He went to Syria, it would seem, after the death of Justin (in 166?). He is charged with holding to the existence of means after the fashion of Valentinus (q.v.), and similar speculations; with an ascetical course of life, carried even to the extent of using water instead of wine; with rejecting marriage as a state of practical fornication; with promulgating Docetic ideas respecting the person of Christ, etc. — all of which must be regarded as substantially a truthful indictment. He would seem, however, to be more nearly related to Saturninus (q.v.) than to Valentinus in his views. The time of Tatian's death is not exactly known, but it seems to have been prior to the date of the work by Irenaeus, Adv. Haer. (c. 175). His most famous work was a harmony of the Gospels, the Diates saron, of which the Jacobite bishop Bar-Salibi (12th century) reports that Ephraem Syrus (q.v.) wrote a commentary on it, and Theodoret the: genealogical tables and all the passages by which the Lord's descent from David is made apparent. The Oratio ad Graec. was first published at Tigur. 1540, fol., and afterwards often. See Daniel, Tatianus, der Apologet. (Halle, 1837); Mohler, Patroologie; Ritter, Gesch. d. christl. Philosophie, vol. 1; Dorner, Person Christi, 1, 438; Moller, Kosmologie d. griech. Kirche, p. 168 sq.; Stockl, Gesch. d. Philos. in d. patrist. Zeit, p. 148 sq.; Huber, Philos. d. Kirchenvoter, p. 20 sq.; Duneker, Apologet; Secund. Sec. de Essential. Naturae Hum. Partibus Placitc (Gott. 1850), pt. 2; and Herzog, Real- Encyklop. s.v. For monographs, see Volbeding, Index Programmatum, p. 104.