Why was it done and by whom?
Originally it was thought that the forts had become vitrified due to an enemy attack. A theory proposed by Childe in the 1930 thought it was that it was invaders, not the builders, who were assaulting the forts and then setting fire to the walls with piles of brush and wood; however, it is hard to understand why people would have repeatedly built defences that invaders could destroy with fire, when great ramparts of solid stone would have survived unscathed. Also this theory does not stand up to the geographic distribution of hill forts versus the known warring area where hill forts were in use. For example the south of England suffered wave after wave of hostile invasion from other Gaullish tribes yet no vitrification has been noted – surely if it was a natural effect of a battle then these forts would be more likely to occur in the south of England (given the large concentration of timber laced ramparts and the frequency of fighting in the area).
This idea was amended with the theory that the builders of the walls had designed the forts in such a way that the vitrification was purposeful in order to strengthen the walls. This theory postulated that fires had been lit and flammable material added to produce walls strong enough to resist the invading armies of the enemy. It is an interesting theory, but one that presents several problems. The main problem with this theory is there is no indication that such vitrification actually strengthens the walls of the fortress; rather, it seems to weaken them. In some cases, the walls of the forts seem to have collapsed because of the fires, however this may show an error in the calculations of the builders.
To further illustrate this point, Julius Caesar described a type of wood and stone fortress, known as a murus gallicus, in his account of the Gallic Wars. This was interesting to those seeking solutions to the vitrified fort mystery because these forts were made of a stone wall filled with rubble, with wooden logs inside for stability. Caesar notes how the flexibility of the wood adds to the strength of the fort in case of battering ram attack.
Some researchers are sure that the builders of the forts caused the vitrification. Arthur C. Clarke quotes one team of chemists from the Natural History Museum in London who were studying the many forts:
“Considering the high temperatures which have to be produced, and the fact that possibly sixty or so vitrified forts are to be seen in a limited geographical area of Scotland, we do not believe that this type of structure is the result of accidental fires. Careful planning and construction were needed.”
Our own research into how forts were vitrified does indeed suggest a deliberate and planned action on behalf of the builders. Looking at the hill forts in evidence today it appears that although many seem to be specifically built in strategic locations some do not take full advantage of the natual defences available. Another common feature is that many vitrified forts have two rings of ramparts, but only the inner is vitrifed. This suggests that the vitrified rampart was for the benefit of the forts users (not visible outside the fort) and that although linked with battle, the vitrification served a purpose other than strengthening the fort.
Beyond this reasoning any further comment is pure speculation, but our research does indicated that the vitrification process could have been part of a lengthy ‘ceremony’ and will have been directed by the most powerful members of the community. Although it is strongly felt that vitrification of forts represents a cultural or religious element, further comment is reserved until further investigative work can be performed.