Citations:keystone


 * 1934 — Anon., All About Shanghai: A standard Guidebook, The University Press, Shanghai. 1983 reed., Oxford University Press, Oxford, ISBN 0-19-581594-7. p. 146;
 * Tartars, Mongols, Mings, and Manchus have, in turn, swayed the empire of which Peiping for so long was the keystone.