Title of a Gospel harmony composed in the 2nd cent.; the first known Gospel translation into Syriac. The title is Greek, meaning ‘through [the] four [Gospels]’. In the Syriac world it was known either by its transliterated Greek name (diyaṭessaron) or as the ewangeliyon da-mḥallṭe (‘Gospel of the mixed’, as contrasted with the ewangeliyon da-mparrše, ‘Gospel of the separated’). The Diatessaron occupied a preeminent position in the Syrian Church in the first four centuries. Aphrahaṭ often appears to cite the Gospels in the form of the Diatessaron. Ephrem composed his Commentary on the Diatessaron. The Syrian-born hymnographer Romanos the Melodist quotes its text in his Greek hymns. Later commentators and writers (e.g., Theodoros bar Koni, Ishoʿdad of Merv, Dionysios bar Ṣalibi, ʿAbdishoʿ bar Brikha) all speak of it with great respect. Bar Brikha even imputes to Tatian an almost mystical grasp of the ‘intention’ of the evangelists, enabling him to accurately harmonize the Gospels without loosing or distorting anything. The evidence of the Teaching of Addai and Bp. Theodoret of Cyrrhus (‘Compendium of Heretical Fables’, I.20) are proof of the Diatessaron’s ecclesiastical, liturgical use into the early 5th cent. Theodoret reports he confiscated ‘more than 200 copies in reverential use in the churches of our diocese’, and replaced the Diatessaron with the four separate Gospels (ewangeliyon da-mparrše). And it must be assumed that Canon 43 of Bp. Rabbula of Edessa, which requires the use of the ewangeliyon da-mparrše in churches, is also directed against the Diatessaron. Eventually the Diatessaron was replaced by the Old Syriac Version of the separate Gospels and, eventually, the Peshitta. Even in these, however, the Diatessaron’s influence is discernable in specific harmonizations and turns of phrase.

Although the origin of the Diatessaron is enshrouded in darkness, it was most likely compiled by Tatian, the author of an ‘Oration to the Greeks’ (preserved in Greek) who describes himself as an ‘Assyrian’ (the exact geographical meaning of which is debated: either Mesopotamia or Syria). After sampling many philosophies in the mid-2nd cent., he converted to Christianity and ended up in Rome where he studied under Justin Martyr. It seems that Justin was already using a Gospel harmony, apparently based on the synoptic Gospels. After Justin’s death (between 163 and 167), Tatian ran afoul of the Roman congregation. Eusebius says that he was expelled from the Roman congregation in 172. After that we have only a report of Epiphanius, stating that he returned to the East, where he founded a school. Given this history, it seems unlikely that Tatian would have created the Diatessaron while Justin (with whom he seems to have had good relations) was alive. Similarly, since no Greek (‘Western’) source speaks of the Diatessaron prior to Eusebius (and Eusebius was an Easterner in practice, and wrote in the East), it seems unlikely that the Diatessaron was composed in Rome. Rather, it is more likely to have been composed on the way back to the East, or in the East, shortly after 172. Evidence suggests that the Diatessaron was composed in Syriac (see below). If correct, this too would favour composition in the East (but it should not be interpreted as precluding composition in the West, for Syriac was used in Rome in the 2nd cent.). While the use of the Diatessaron in early Syriac Christianity presupposes an early date for its composition, Tatian’s authorship is not explicitly mentioned in any of the early Syriac sources. Not surprisingly, therefore, his authorship has been questioned in recent research (Koltun-Fromm).

A Gospel harmony is a complicated creation. It seeks, by acute literary skill, to conflate parallel accounts. Duplications are excised, conflicts are resolved, and nothing of importance is lost. Various reasons for Tatian’s efforts have been suggested; none, on its own, is convincing, and the reality probably lies in a combination of motives. First, in his only other surviving literary work, his ‘Oration to the Greeks’, Tatian emphasizes the unity of truth. Four canonical Gospels as well as numerous extra-canonical Gospels do not present a ‘unity’ which, for Tatian, was the hallmark of truth. Here, then, one can discern a motive for creating a single, harmonized account. Second, the contradictions and inconsistencies in the Gospels had led critics such as Celsus to ridicule Christianity. One way to resolve these problems was Marcion’s: to select one gospel and exclude all others. But the same problem may also be solved as Tatian did: create one Gospel — a harmony — out of the many. A third motive may simply have been the spirit of the times. Tatian’s teacher Justin used a harmony, and other harmonies circulated in the early Church. In other words, Tatian may simply have been doing what others were doing. Fourth, the 2nd-cent. view of the task of an historian was to sift through the sometimes contradictory individual accounts of an event and then, through the exercise of sound historical judgement, write the single definitive account. According to this view, Tatian saw himself as an historian; the Gospels were ‘raw material’ for an historian; the Diatessaron was therefore a scholarly work of a ‘professional’ historian.

The Diatessaron is extremely important for recovering the oldest text of the Gospels. It is obvious that Tatian, when composing his harmony, had to use the Gospels in the form they had in the mid-2nd cent. He also, apparently, availed himself of Justin’s already-extant harmony of the synoptic Gospels, augmenting it with material from the Gospel of John and then recasting its sequence. Therefore, the Diatessaron preserves numerous ancient deviating readings — that is, readings which deviate from modern critical editions of the Gospels, but which agree with other 2nd- cent. sources (such as the Jewish-Christian Gospel fragments, the ‘Gospel of Thomas’, Justin, etc.). This means that when he composed the Diatessaron, Tatian either used (proto-) canonical Gospels whose text contained readings now found only in the Jewish-Christian Gospels, or that, in addition to the canonical Gospels, he also used extra-canonical sources, including one or more Jewish-Christian Gospels.

Today no direct copies of the Diatessaron survive. Its text must be reconstructed through a painstaking collation and comparison of numerous ‘witnesses’ to the Diatessaron: an assortment of translations (into both Eastern and Western languages) and patristic quotations. These include translations (sometimes heavily revised) into Arabic, Latin, Old Italian, Old High German, Middle Dutch, Middle High German, Middle English, and other languages. A Persian harmony also exists, but its sequence is very different from that of the Diatessaron, even though in many individual variants it seems to agree with the Diatessaron. It should be noted that a gospel harmony has two distinctive features which can be used for identification: 1. the sequence of harmonization, and 2. the individual variant readings within a verse.

The Diatessaron’s influence was not limited to Syria, but extended to other areas, both Eastern and Western. It is thought that the Gospels first appeared in Armenian in the form of a translation of the Diatessaron, and it influenced the translation of the separate Gospels into Georgian. We even find its distinctive readings in the Manichaean texts written in Parthian and found at Turfan, in China. In the West, the oldest known translation of the Gospels into Middle Dutch is a Gospel harmony (known as ‘the Liège Harmony’) related to the Diatessaron; and while not the oldest Gospel translation into Old High German (that honour goes to a few fragments at a cloister in Mondsee, Austria), a Gospel harmony related to the Diatessaron, Codex Sangallensis, is the oldest complete Gospel text in Old High German.

It is on the basis of these Western witnesses to the Diatessaron that one can reach a judgement about its original language. The presence of Syriacisms or Semitisms in these ‘Western’ witnesses to the Diatessaron can only be explained by presuming that their archetype was a document composed in a Semitic language, not Greek or Latin.

Because of the Diatessaron’s paramount importance for both the text and canon of the NT, much scholarly effort has gone into reconstructing its text. Equally important, however, is its position as the oldest of the versions, a translation and rearrangement of the Gospels that had world-wide impact, from England to China.