"Gunnery". Encyclopædia Britannica. London. 1771.
J. G. Benton (1859). Ordnance & Gunnery. U.S. 2010 Military Academy.
Dupuy, Trevor Nevitt (1990). The Evolution of Weapons and Warfare. New York: Da Capo Press. p. 219. ISBN 0-306-80384-4. 0-306-80384-4
Illustration of trebuchet by Kolderer, c1507, as reproduced at Medieval Siege Technology and Countertechnology by Andrew Vick. http://web.grinnell.edu/courses/ant/S00/ANT154-01/vick/treb.html
This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al. {{cite encyclopedia}}: Missing or empty |title= (help) /wiki/Public_domain