During a new fear of invasion from Napoleon III two new dry moats were added to the existing citadel defences. The northern and the southern moat both had their own casemates built. Between these, there was also a defensive caponier built, but sadly this was filled in during the 1960s by the Dover Corporation and they gradually destroyed many parts of the Western Heights.

The southern casemates are a lot larger than the northern casemates, with eight separate rooms whereas the northern casemates only had six.