The ritual of oak and mistletoe is a Celtic religious ceremony, in which white-clad druids climbed a sacred oak, cut down the mistletoe growing on it, sacrificed two white bulls and used the mistletoe to make an elixir to cure infertility and the effects of poison. The ritual, known from a single passage in Pliny's Natural History, has helped shape the image of the druid in the popular imagination. Engraving by Simon Francois Ravenet entitled: The Druids, or the Conversion of the Britons to Christianity. Image taken from Druidism: The Ancient Faith of Britain by Dudley Wright, 1924 (cropped and cleaned).