At http://popular-archaeology.com/issue/winter-2015-2016/article/some-iron-… … we've heard of the vitrified forts of Scotland where timbers were set alight to partially melt stones and rocks but now it seems archaeologists are thinking in terms of this practise being quite common – on the continent and even in northern England. However, in southern Britain hill forts are usually made of earth ramparts with ditches, and presumably this was common on the continent as well. The burning process was previously attributed to unfriendly fire – evidence of violent onslaught. Now one can't jump to that conclusion without first ruling out friendly fire – purposeful torching.
The study is published in the Journal of Archaeological Science February 2016.