In his article 'Theory and Practice in the Vergilian Cento' (ICS 9, pp. 79-90), David F. Bright points out (p. 83 and n. 20) that, when the prologue is subtracted, Proba's cento (in which Vergil is Christianized) has exactly 666 lines. I had not noticed this fact; Bright remarks on it because it has bearing on his statistical analysis (the 29-line prologue is only partly centonic). This number, of course, has obvious Christian significance. Here is the Vulgate version of Revelation 13:18 (not the version Proba would have known, but it will at least give us some Latin):
hic sapientia est qui habet intellectum conputet numerum bestiae numerus enim hominis est et numerus eius est sescenti sexaginta sex
It is odd that the fully Vergilian part of the poem is exactly coterminous with the Number of the Beast. Coincidence? Or is Proba here attempting a poetic neutralization, appropration, and 'redemption' of more than just Vergil?