Perhaps in the early 1470s, and certainly by the end of the decade, Leonardo became very interested in the movement of water through man-made, technical means. Vasari states that Leonardo, when “still a youth,” was the first to suggest reducing the unpredictable river Arno to a navigable canal from Pisa to Florence. The earliest pages (c. 1478–80) of Leonardo's Codice Atlantico are covered with devices for raising large quantities of water or directing its flow. Some sheets credibly illustrate systems of weirs and locks on canals; others have studies of contraptions with gears, weights, and hydraulic cylinders, such as the so-called Archimedes’ screw, based on the ancient Greek mathematician's famous invention, which supposedly employed a large revolving spiral to pull water upward (fig. 7). Although Leonardo's writings indicate that he sometimes consulted treatises on water in Lorenzo the Magnificent's possession, the latter seems not to have kept in his library any books by Archimedes or Heron of Alexandria, the two standard, classical sources on hydrostatics and pneumatics. However, Leonardo probably saw a copy of the Italian humanist Roberto Valturio's De re militari (1472), an anthology of ancient military science, which illustrated the hydroscrew and other devices for the conveyance of water. The artist would eventually obtain his own version of this text.