Tatian the Syrian is important in many ways for understanding the paths taken by the theology of the early Church. His apologetic work was methodologically different from other apologists of his time. While Justin, Athenagoras, Clement, Melito and others were trying to show how Christianity is acceptable to the Greeks, Tatian wants to show his superiority. His Diatessaron provided him a permanent and respected place in the memory of the Churches of the East. On the other hand, his encratism, as well as specific understandings of the Logos, the soul and the place of the Old Testament in the Christian tradition, classify him among heretics. Therefore, the analysis of his teachings is a necessary element of understanding the developmental paths of ancient theology.