This is another one from The Once and Future King, by T.H.White. It is evident from the text that this word relates to warfare or at the very least defense--I'm apparently too lazy to go and look up the exact quote right now. However, I am not too lazy to relate that the only connection I have to the word 'barbican' is "The Barbican School of Modeling", which, unless modeling is a much more aggressive skill than I've been led to believe, is puzzling, to say the least...
Well, thanks to the internet, we actually have easy access to things like "The T.H. White glossary", which will not only happily provide us a definition of 'barbican', but actually cite the page reference, so that I can now quote the sentence it appeared in. Page 41: "The stone part of the drawbridge with its barbican and the bartizans of the gatehouse are in good repair."
I'd noted that "bartizan" in reading, but thought I could gloss over it. Apparently not.
First, let us go to that old Barbican School of Modeling reference, for I feel sure I have now found its source. I actually haven't been so successful finding any listing for such a school, but any reference obviously is trying to link to the Barbican Theatre in London, and get a "posh" connotation by inference. The Barbican Centre in London is all about theatre, dance, music and the like, and so actually rather far from the original definition of the word.
"A tower or other fortification on the approach to a castle or town, especially at a gate or a drawbridge." (thanks, Freedictionary.com!)
But a certain Pettifer at the T.H. White site goes a little further: "An outer extension to a gateway, increasing the number of barriers which a besieger had to force his way through. The commonest type of barbican is a walled passage projecting from the front of the gatehouse proper."
Got it? Good. Because now we are on to 'bartizan', which the White glossary refers to as "a small turret corbelled out at parapet level, usually at the corners of a tower."