The Druids, even in Gaul, where they were not altogether ignorant of the use of letters, in order to preserve their knowledge in greater respect, committed none of their precepts to writing.

The proficiency of their pupils was estimated principally by the number of technical verses which they retained in their memory: a circumstance that shows this discipline rather calculated to preserve with accuracy a few plain maxims of traditionary science than to improve and extend it.

And this is not the sole circumstance which leads us to believe that among them learning had advanced no further than its infancy.
The scholars of the Druids, like those of Pythagoras, were carefully enjoined a long and religious silence: for, if barbarians come to acquire any knowledge, it is rather by instruction than, examination; they must therefore be silent.

Pythagoras, in the rude times of Greece, required silence in his disciples; but Socrates, in the meridian of the Athenian refinement, spoke less than his scholars: everything was disputed in the Academy.
The Druids are said to be very expert in astronomy, in geography, and in all parts of mathematical knowledge; and authors speak in a very exaggerated strain of their excellence in these, and in many other sciences.

Some elemental knowledge I suppose they had; but I can scarcely be persuaded that their learning was either deep or extensive.
In all countries where Druidism was professed, the youth, were generally instructed by that order; and yet was there little either in the manners of the people, in their way of life, or their works of art, that demonstrates profound science or particularly mathematical skill.
Britain, where their discipline was in its highest perfection, and which was therefore resorted to by the people of Gaul as an oracle in Druidical questions, was more barbarous in all other respects than Gaul itself, or than any other country then known in Europe.