A gazetteer compiled by archaeologist Robert Higham counted 21 shell keeps in England and Wales.1 Examples include the Round Tower at Windsor Castle23 and the majority were built in the 11th and 12th centuries.4
Surviving English examples of shell keeps include:
In addition Farnham and Berkeley castles have stone enclosed mottes which may be interpreted as shell keep variations. At other sites such as Durham, Warkworth, Clifford's Tower (York) and Sandal (Wakefield), shell keeps may have evolved into a tower proper. Clifford's Tower is often interpreted by modern visitors as a shell keep due to explosion damage, in 1684, which removed the roof and its central supporting masonry. True shell keeps were a stone wall around the upper perimeter of the motte with lean-to buildings against this outer wall and a small courtyard in the middle. See Restormel plan below.
Unusually Lewes and Lincoln castles both feature two separate mottes which may have had shell keeps upon both of them. The reason for this is unclear but given that Lincoln Castle is adjacent to the cathedral, one shell keep may have been for the castellan (castle holder) and the other for the bishop. In each case, only one shell keep survives.
Higham 2016, p. 63. - Higham, Robert (2016). "Shell-keeps revisited: the bailey on the motte?" (PDF). Castle Studies Group. http://www.castlestudiesgroup.org.uk/Shell%20Keeps-Essay-low-resRev22a.pdf ↩
Pettifer 2002, p. 7. - Pettifer, Adrian (2002). English Castles: A Guide by Counties (Illustrated ed.). Boydell & Brewer. p. 7. ISBN 0-85115-782-3. https://books.google.com/books?id=47iheRUGKIEC&pg=PA7 ↩
Darvill, Stamper & Timby 2002, p. 196. - Darvill, Timothy; Stamper, Paul; Timby, Jane (2002). England: an Oxford archaeological guide to sites from earliest times to AD 1600 (illustrated ed.). Oxford University Press. p. 196. ISBN 0-19-284101-7. https://books.google.com/books?id=3tMrajZuWR0C&pg=PA163 ↩
Hislop 2013, p. 96. - Hislop, Malcolm (2013). How to read castles. London: Bloomsbury Academic. ISBN 9781472521613. ↩