Pike, David L. (2005). Subterranean Cities: The World Beneath Paris and London, 1800-1945. Cornell University Press. p. 234. ISBN978-0-801-47256-5.
Harvey A. Levenstein, We'll Always Have Paris: American Tourists in France since 1930, Chicago: University of Chgicago, 2004, ISBN9780226473789, p. 31.