Well, Guest this site indicates that extant examples of Ogham date from after the onset of the Christian era, and says that "speculation exists" that the form may pre-date 100 AD. So, in my humble opinion, what you have, Guest, is your own theory regarding Celts originating a written alphabet pre-dating the monks, and therefore I will stand challenged, not "corrected", in my assertion. If you have concrete evidence you can present, it may change my opinion.

And I appreciate your view of Markale as a "Celtic Romantic". My contention is that there is nothing on the U of T page that flies in the face of my earlier summation of his theories, particularly in the "Celtic History" section on the U of T site. In fact, that section bears out my basic contention regarding the speculative nature of Celtic History....the primary sources for information on the U of T site are contemporary Roman historians who perceived the Celts on the whole as deranged madmen, and while they were often able to describe attributes of behavior in battle (which they may have observed), their speculations regarding custom, history, origins etc must be approached with at least as much scepticism as Markale's assertions.