The best-known goals of the alchemists were the transmutation of common metals into gold (called chrysopoeia) or silver (less well known is plant alchemy, or "spagyric" wink ; the creation of a "panacea", or the elixir of life, a remedy that, it was supposed, would cure all diseases and prolong life indefinitely; and the discovery of a universal solvent.[8] Although these were not the only uses for the discipline, they were the ones most documented and well-known. Certain Hermetic schools argue that the transmutation of lead into gold is analogical for the transmutation of the physical body (Saturn or lead) into (Gold) with the goal of attaining immortality.[9] This is described as Internal Alchemy. Starting with the Middle Ages, Persian and European alchemists invested much effort in the search for the "philosopher's stone", a legendary substance that was believed to be an essential ingredient for either or both of those goals. Pope John XXII issued a bull against alchemical counterfeiting, and the Cistercians banned the practice amongst their members. In 1403, Henry IV of England banned the practice of Alchemy. In the late 14th century, Piers the Ploughman and Chaucer both painted unflattering pictures of Alchemists as thieves and liars. By contrast, Rudolf II, Holy Roman Emperor, in the late 16th century, sponsored various alchemists in their work at his court in Prague, one of which was a particular alchemist named Edward Kelley.