You wont find Fort Lizard listed as one the Napoleonic Forts that Guarded Medway and Chatham dockyard during the 19th Century,that's because it wasn't one.It is a nick name given by local people to some tunnels at the bottom of chatham Hill under Mount Pleasant.(by Luton Arches)There used to be some Houses and shops in front of the Tunnel entrances called Caroline Terrace.
There's one bricked up Arch entrance and a small cave like entrance that had a chalk boulder in (now sealed)Supposedly there is another entrance behind the Advertising Boards but i've never seen this one.
As to what the tunnels were for,if they were connected at all,how far into the hill they went,and if there used to be another entrance on top of the hill on the Great Lines is a bit of a mystery.
I have put some possible theories of what the tunnels were for and some of my personal opinions below:
1) Storage for the Houses/Shops that used to be there.
2) Air-raid shelters.
3) Old tunnel to Medway Maritime Hospital -used as a quick way up to the nearby Hospital on top of the Hill.
4) Old access Tunnel to The nearby Railway tunnel under the Great Lines.
5) Old Military Tunnel - used to climb the Hill quickly and out of site.
6) Tunnel to fort Amherst - I very much doubt it though.
7) Old Chalk Mine.
There are people who claim to have been in the Tunnels as Kids and even some rumours they are quite big,but we can't be sure of the truth in this.The tunnels may even be no more than a few metres big,so unless some plausable information comes to light they will remain a bit of a mystery...