It is difficult for us to realize that in the ancient Irish Schools of Poets the students were trained in not less than three hundred and fifty different kinds of metre. Twelve years was the minimum period of study in the schools. There were four grades of poet -- each requiring three years of concentrated study. Each grade was sub-divided again many times. Of the lowest grade, the bard, there were sixteen divisions distinguished by the metres they had mastered. As instance of the prosodial subtlety and complexity of the metres, let us instance that of one kind alone, the nath metre which was mastered by the king-bard, there were six different kinds, and these six again divided, some of them into as many as six subdivisions. Therefore, it was an arduous task which arose before the Irish poetic aspirant -- and wonderful and powerful was the mental training through which the Irish poet passed.
The poet's course in literature embraced seven times fifty of the great bardic epics -- all of which he must not only have memorized, but have mastered in every detail -- and with each of which, when called upon, must be able to hold spellbound every gathering. Furthermore, when he should go for his final degree he must be able to compose an impromptu short poem on any subject suggested. The poet-ollam, the poet of highest rank, must be a master of Irish history, Irish antiquities and genealogies of all the leading Irish families -- and always able and ready at a moment's notice, to recite anything called for in any of these subjects. Few and far between are the twentieth century scholars who are as thoroughly steeped in their subjects as were the poet-ollams of fifteen hundred years ago.
The Story of the Irish Race, by Seumas MacManus (The Devin-Adair Company: New York, 1944/1967) page 179-180.
Such a regiment of training for a poet, has been used in more recent times as a metaphor for poetic development. An example of this is chronicled in the well-known though anthropologically goofy work by Robert Graves, The White Goddess: A Historical Grammar of Poetic Myth (New York: The Noonday Press, 1973 ).