Thanks fer that, funnily enough, I was thinking abut these forts the other day. I first became aware of them as a nipper cos of the Arthur C Carke prog 'Mysterious World...In fact, here's the short vid.....
Vitrified Scottish Forts from "Arthur C. Clarke's Mysterious World" (1980)
https://www.youtube.com/watch?v=jUb5212SCls

There's a brief overview similar, though less techy than the Nature article here....https://news.nationalgeographic.com/2016/03/160303-archaeology-history-forts-vitrification/