Detail of the C12th century bailey walls
see http://www.castlefacts.info/castledetails/castleDetails3.aspx?uin=11540
see http://en.wikipedia.org/wiki/Hertford_Castle
see http://www.hertford.gov.uk/Hertford-Castle----a-unique-venue-4435.asp?page=4435
see http://www.ecastles.co.uk/hertford.html