Few areas of castle studies are so poorly understood as 'adulterine castles', and particularly the nature of the castles built in the reign of King Stephen and 'destroyed' in the reign of Henry II. The effect of this misunderstanding on the dating of many early and less well known castle sites is quite profound. This paper by Charles Coulson explains the problems and elucidates the difficulties in interpretation of the medieval sources. Essential reading for anyone interested in early castles in particular and for all people involved in using medieval sources of any date in their castle studies.
Reprinted in Liddiard, Robert (ed), 2003, Anglo-Norman Castles (Boydell Press) pp. 179-202 which contains many other important essays for castle studies.