The term diatessaron was in fact a major concept in Pythagorean musical theory (much of the theory of Greek music was believed to have been invented by the Pythagoreans). It was thought to embody musically the sacred Pythagorean tetraktys, the fundamental equation containing the four smallest whole numbers: 1 + 2 + 3 + 4 = 10. The number 10, called the "decad," was thought to be the perfect number symbolizing the entire universe. Did this Pythagorean concept influence Tatian? Possibly. Just as Justin used the Platonic/Pythagorean concept of memoirs to the three Christian Gospels he had harmonized, Tatian might have selected the Platonic/Pythagorean term diatessaron to identify his new fitting together of the four sacred books "of the barbarian philosophy.
Would Tatian have been aware of the Pythagorean connotations of this term in Syria-Palestine at this time? Possibly. Although Pythagorean speculation had died down somewhat during the centuries after Plato, there was a great revival of interest in Pythagorans and things Pythagorean in the first and second century CE. In Syria, three decades prior to Tatian's return, a leading Pythagorean philosopher and mathematician named Nicomachus of Gerasa (60-145 ce), published a treatise entitled Hand- book on Harmony that discussed all of these terms, discussed all of these terms, giving them deep religious significance. For example, chapter three is dedicated to the relationship between the harmonious sound of the planets and human music: "Among objects of perception, the music associated with the planets is considered to be the prototype of our music according as we imitate it. [A History of the Synoptic Problem p. 41]
Of course, Dungan assumes that Tatian is the harmonizer of four gospels and skips over the obvious connection of Clement of Alexandria to Philo 'the Pythagorean' as Clement refers to him. The skipping over of Philo in favor of Nichomachus is utterly forced and makes it seem as if the Pythagorean revival only started in the second century. But such is the way of scholarship.
Dungan's work is still significant and an endnote to this section is worth citing too:
tetrakyts - 1, 2, 3, 4 — which contained all the components of 6:8:9:12 extended over two full octaves, for it comprises 1:2 (6:12), the lower octave; 2:3 (6:9), the fifth; 3:4 (6:8), the fourth; 2:4 (6:12), the upper octave and 1:4, the double octave." All of this would have been rich with significance. Oddly, in his monumental study of Tatian's Diatessaron, Theodore Zahn missed the possible Pythagorean connection completely, although he did notice that the term was a terminus technicus from Greek music; see Zahn, Tatian's Diatessaron: Forschungen zur Geschichte des neutestamentlichen Kanons und der altchristlichen literature, I Theil (Erlangen: Verlag Andreas Deichert 1881) 239
