Just read (quite quickly, so forgive any duplication of ideas!) the whole thread, and I'dlike to add my two pennorth!

Suppose the builder of such forts are under imminent attack from a larger force. Judging by the layout of Brigs maps of dykes etc, we'rre looking a t a large area to be defended. Consider the possibility that an engineer/mage/druid/smartass from the tribe or from another land has introduced the technique of Greek Fire (or similar). No matter how strong the ramparts or how numerous the defenders, the invaders may be in a position to storm the defences and gain access. If the builders/defenders, anticipating an attack have prepared the walls using flammable materials, when the tribe advances on the fort, torches could be used to ignite the walls - thereby creating A) an impassable sheet of flame B) and impressive display C) a fiery Beacon to warn neighbouring forts/settlements D) Light to see by during a night attack E) hot slippery walls which would be difficult to scale.
F) Something to toast your buns on while waiting for the attackers to piss off home!

What say?