Colin A. Ronan, The Shorter Science and Civilisation in China, Volume 5 of The Shorter Science and Civilisation in China: An Abridgement of Joseph Needham's Original Text, illustrated, Cambridge University Press, 1995, p. 250, ISBN 0-521-46773-X. URL consultato il 28 novembre 2011.
«Moreover, many Chinese were in the first wave of the Mongolian conquest of Iran and Iraq - a Chinese general, Guo Kan, was first governor of Baghdad after its capture in ad 1258. As the Mongols had a habit of destroying irrigation and»