was famous. Cicero, who attaches considerable importance to the art, but more to the principle of order as the best help to memory, speaks of Carneades (perhaps Charmades) of Athens and Metrodorus of Scepsis as distinguished examples of people who used well-ordered images to aid the memory. The Romans valued such helps in order to support facility in public speaking. The Greek and the Roman system of mnemonics was founded on the use of mental places and signs or pictures, known as "topical" mnemonics. The most usual method was to choose a large house, of which the apartments, walls, windows, statues, furniture, etc., were each associated with certain names, phrases, events or ideas, by means of symbolic pictures. To recall these, an individual had only to search over the apartments of the house until discovering the places where images had been placed by the imagination. In accordance with this system, if it were desired to fix a historic date in memory, it was localised in an imaginary town divided into a certain number of districts, each with ten houses, each house with ten rooms, and each room with a hundred quadrates or memory-places, partly on the floor, partly on the four walls, partly on the ceiling. Therefore, if it were desired to fix in the memory the date of the invention of printing (1436), an imaginary book, or some other symbol of printing, would be placed in the thirty-sixth quadrate or memory-place of the fourth room of the first house of the historic district of the town. Except that the rules of mnemonics are referred to by Martianus Capella, nothing further is known regarding the practice until the 13th century. Among the voluminous writings of Roger Bacon is a tractate De arte memorativa. Ramon Llull devoted special attention to mnemonics in connection with his ars generalis. The first important modification of the method of the Romans was that invented by the German poet Conrad Celtes, who, in his Epitoma in utramque Ciceronis rhetoricam cum arte memorativa nova (1492), used letters of the alphabet for associations, rather than places. About the end of the 15th century, Peter of Ravenna (b. 1448) provoked such astonishment in Italy by his mnemonic feats that he was believed by many to be a necromancer. His Phoenix artis memoriae (Venice, 1491, 4 vols.) went through as many as nine editions, the seventh being published at Cologne