Diatessaron. – A work by Tatian, which fused the text of the four Gospels into a single coherent narrative. This fact is reported to us by the historian Eusebius (Hist. eccl., IV, 29) and by other ancient writers. Of the work, the following have come down to us: 1) a brief Greek fragment, discovered in 1933 among the ruins of Dura Europos on the Euphrates; 2) fragments of a Syriac version in quotations by Syriac writers and in the commentary of St. Ephrem (which has come down to us in Armenian); 3) a complete Arabic version from the Syriac, from the 11th century (v. ABU 'I-FARAG 'ABDALLAH IBN AT-TAY'IB); 4) a complete Latin reworking in the Fulda codex of the Vulgate, from which descend or are collateral several medieval Gospel harmonies in Latin, Italian, German, Dutch, and English.
As for the order of the material, i.e., of the Gospel events, documents 2°–4° do not agree exactly, but they concur in what is characteristic and essential of Tatian’s arrangement, namely, that, based on the framework of the Passovers mentioned in the Fourth Gospel, which he inverts in the traditional chapters 5 and 6, he reduces the public life of Jesus to a year and a few months, and groups all of Jesus’ activity in Jerusalem toward the end around the day of Palm Sunday. They also all agree in placing the washing of the feet before the Paschal supper and Judas’ departure before the institution of the Most Holy Eucharist. As for the rest, the best witness, though incomplete, of the original order seems to be the commentary of St. Ephrem, followed by the Arabic version; the Western branches diverge more from II.
As for the textual wording, the situation is even worse. The Arabic version presents us with a Syriac text already conformed, in its material expression, to the Peshitta, i.e., to a version made in the 5th century from the Greek then current in Antioch (v. BIBBIA). In the codex of Fulda, Victor of Capua (c. 546) replaced the primitive Latin translation with the Vulgate of St. Jerome (382). The genuine text of Tatian is better preserved for us, though fragmentary and in a third-hand form, in the commentary of St. Ephrem and in the scant quotations of other Syriac writers. Hence the delicacy of the problems in using Tatian for the textual criticism of the Gospels.