During his prolonged stay in Rome, according to his own representation, his abhorrence of the pagan cults sparked deep reflections on religious problems.
[11] Epiphanius relates that Tatian established a school in Mesopotamia, the influence of which extended to Antioch in Assyria, and was felt in Cilicia and especially in Pisidia.
His Oratio ad Graecos (Address to the Greeks) condemns paganism as worthless, and praises the reasonableness and high antiquity of Christianity.
As early as Eusebius, Tatian was praised for his discussions of the antiquity of Moses and of Jewish legislation, and it was because of this chronological section that his Oratio was not generally condemned.
A fragment of a narrative about the Passion found in the ruins of Dura-Europos in 1933 was once thought to have been from the Diatessaron, but more recent scholarly judgement does not connect it directly to Tatian's work.
The earliest member of the Western family of recensions is the Latin Codex Fuldensis, written at the request of bishop Victor of Capua in 545 AD.
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.
Unlike Justin, who had related the new Christian doctrine to philosophy, Tatian manifests a violent rejection of the forms of philosophical literature with which he is familiar and consequently turns to a safer literary genre: the writing of history.
Tatian claims that the Greeks learned historiography from the Egyptians (Oratio ad Graecos 1.1), who possessed exact techniques for chronology (38.1).
For the Syriac the Greeks are skillful literati, bad philosophers, but they can never be good historians, for "for those who have a disjointed chronology it is impossible to say what is true of history" (31.4).
He also distinguishes between annals and documents that are within the historian's reach and things that fall outside his direct knowledge (Oratio ad Graecos 20.2), another of Thucydides' principles.
Another characteristic of the rigorous historian is the personal inspection of places and cities with the discernment of the various types of documentation and sources: Well then, all these things I do not expound because I learned them from another but because, traveling through many lands I have been a teacher of your own doctrines and have examined many arts and conceptions and finally I was able to study with attention the variety of statues brought by you to the city of Rome.
For I do not seek to confirm my doctrines, as the vulgar do, with opinions foreign to my own, but 'I wish to compose anagraphs' (τὴν ἀναγραφὴν συντάσσσειν βούλομαι) on all those things which by myself I have understood (Oratio ad Graecos 35.1).What Tatian seems to propose is thus not a philosophy, theology, or exegesis of some revealed text, but a historical truth that attentive study can achieve.
For the first time the voice μυθολογία appears in the Christian lexicon (Oratio ad Graecos 40.1); it specifically signifies the falsification of the philosophy of Moses perpetrated by the Greeks.
Their poetry is shameful but, nevertheless, not false in an absolute way, because the 'gods' exist and act: they are the 'demons', who impinge on the deviation of human behavior and are the ones who manage the destructive and evil culture of the whole Greek παιδεία.