Although since Christian times Druids have been identified as wizards and soothsayers, in pre-Christian Celtic society they formed an intellectual class comprising philosophers, judges, educators, historians, doctors, seers, astronomers, and astrologers. The earliest surviving Classical references to Druids date to the 2nd century B.C.E. The word Druidae is of Celtic origin. The Roman writer Pliny the Elder (Gaius Plinius Secundus, 23/24-79 C.E.) believed it to be a cognate with the Greek work drus, meaning "an oak." Dru-wid combines the word roots "oak" and "knowledge" (wid means "to know" or "to see" - as in the Sanskrit vid). The oak (together with the rowan and hazel) was an important sacred tree to the Druids. In the Celtic social system, Druid was a title given to learned men and women possessing "oak knowledge" (or "oak wisdom").
Some scholars have argued that Druids originally belonged to a pre-Celtic ('non-Aryan') population in Britain and Ireland (from where they spread to Gaul), noting that there is no trace of Druidism among Celts elsewhere - in Cisalpine Italy, Spain, or Galatia (modern Turkey). Others, however, believe that Druids were an indigenous Celtic intelligentsia to be found among all Celtic peoples, but were known by other names.
With the revival of interest in the Druids in later times, the question of what they looked like has been largely a matter of imagination. Early representations tended to show them dressed in vaguely classical garb. Aylett Sammes, in his Britannia Antiqua Illustrata (1676), shows a Druid barefoot dressed in a knee-length tunic and a hooded cloak. He holds a staff in one hand and in the other a book and a sprig of mistletoe. A bag or scrip hangs from his belt.
