Taipei: Caves Books Ltd.,1986 ISBN 0-521-07060-0* Spruytte, J., Littauer, M.," Early Harness Systems", Hyperion Books, 1990* Riddle, John M.," A History of the Middle Ages, 300-1500", Rowman & Littlefield, 2008* Wigelsworth, Jeffrey R., "Science and technology in medieval European life", Greenwood Publishing Group, 2006
Taipei: Caves Books Ltd.,1986 ISBN 0-521-07060-0* Riddle, John M.," A History of the Middle Ages, 300-1500", Rowman & Littlefield, 2008* Wigelsworth, Jeffrey R., "Science and technology in medieval European life", Greenwood Publishing Group, 2006