Quintilian on C

On pg. 58 in discussing the pronunciation of as a voiceless velar stop, I might have mention this passage from Quintilian (Inst. 1.7.10) where Quintilian mentions that he thinks the letter k should only be used in those words which can be abbreviated by k alone (e.g. K for Kalendae, Kaeso, etc.):

Hoc eo non omisi quod quidam eam quotiens a sequatur necessariam credunt, cum sit c littera, quae ad omnis vocalis vim suam perferat.

I mention the fact because some hold that k should be used whenever the next letter is an a, despite the existence of the letter c which maintains its force in conjunction with all the vowels. [Translation H. E. Butler, Loeb edition]

This clause [quae ad omnis vocalis vim suam perferat] might be taken to mean that c had no significant allophones and therefore that c was still a voiceless velar stop before a front vowel.  Fantasy image of Quintilian from the 15th century Nuremberg Chronicle.