If such an attitude prevailed in the Greco-Roman world this may explain why professional magicians, such as Simon Magus, were on the lookout for new ideas. Pliny devotes the beginning of Book 30 of his work to the magi of Persia and refers to them here and there especially in Books 28 and 29. Pliny defines the Magi at times as sorcerers, but also seems to acknowledge that they are priests of a foreign religion, along the lines of the druids of the Celts in Britain and Gaul. According to Pliny, the art of the magi touches three areas: "healing," "ritual," and "astrology."