Hippocrates and Galenos, the leading medical doctors of their times and creators of the theory that many diseases are of poisonous origin. Thirteenth century fresco in the crypt of the Domo of Anagni near Rome, Italy. The theoretical and therapeutic concepts of these two masters dominated European medical education and practice until the seventeenth century. The text on the paper in front of Galenos (left) reads "Mundi presentis seres manet ex elementis", meaning "The present world's connection persists on the basis of the elements". The text on the paper in front of Hippocrates (right) reads "Ex his formantur que sunt quecu(m)q(ue) chreantur", meaning "Of these (all) is formed which exists and which will be created". The four basic elements were represented by air, fire, earth and water. Image courtesy of the Art Archive/Anagni Cathedral Italy/Dagli Orti (A).