Thompson's classic is dated now, as an emphasis on the castle as a military structure shows, but continues to be worth reading.
The Dover edition, first published 2005, is an unabridged republication of the work originally published in 1912 by Oxford University Press, London, under the title Military Architecture in England during the Middle Ages.
For biographical notes see
Kenyon, John R., 2012-13, 'Alexander Hamilton Thompson (1873-1952)' The Castle Studies Group Journal Vol. 26 p. 253-4
