(Bugger, got the spelling wrong in the title)
I was listening to a Levellers song earlier today that had the line 'They didn't build Jerusalem'' and it got me thinking about the occurances of 'Jerusalem' in English folklore. There is of course the hymn and I've heard a CB+S song called Jerusalem Revisited about failings in society etc.

I would theorise that this originates from the Crusades and the Jerusalem is ment to signify a sort of 'perfect society', holy and just and free etc.

Any thoughts/ideas/info?