I have at last finished the first installment of my exploration into vitrified forts. I have not got 12 forts in my gazeteer and think I can explain how they were vitrified, but not (at this moment) why.

Thanks to all who contributed the URL is:

http://www.brigantesnation.com/VitrifiedForts/VitrifieedForts.htm

Thanks to your help I have now created the world's first gazetteer of vitrified forts as well as a detailed explaination of what is known about them, together with a much clearer understanding of them.

PS - 12bar - I got 100! expect burnt mounds soon!