Medieval Fortifications, John R. Kenyon, Leicester University Press, Great Britain, 1990.

Castles in Britain, W. Douglas Simpson, B.T. Batsford Ltd, London, 1966.

Military Architecture in England during the Middle Ages, A. Hamilton Thompson, Oxford University Press, London, 1912.

The Architecture of Castles: A Visual Guide, R. Allen Brown, B.T. Batsford Ltd, London, 1984

Cross-Sections Castle, by Stephen Biesty & Richard Platt, Dorling Kindersley Publishing, Inc., New York, New York, 1994. (pictures)

The World Book Encyclopedia, (Articles on England, France, Scotland, Germany,  Castle, Feudalism, Manorialism,) World Book Inc., Chicago, IL, 1993.

Codesmiths, http://www.codesmiths.com/siege/ (photos)

The Online Reference Book for Medieval Studies, http://orb.rhodes.edu/

The Castles of Britain, http://www.castles-of-britain.com/ (photos)

Bibliothèque National de France - The Age of King Charles V, http://www.bnf.fr/enluminures/aaccueil.htm