Aristotle (-384 to -322) wrote that the Druids were the first philosophers of the world, corroborating the earlier opinion of Pythagoras (-582 to -507) that they were the wisest men ever. Iamblichus (d.-326) stated that Pythagoras had been "initiated into the ancient wisdom" during his stay amongst the Druids. The Druids originated from amongst the Celts, for Pliny the Elder records that "the barbarous Celts learnt the cult of the oak from the refined Greeks".