Vitrified forts — How and why?

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BrigantesNation B
BrigantesNation May 14, 2002 09:11:07
Replying to BrigantesNation

Hamilton describes another vitrified fort that is much larger, situated on the island at the entrance of Loch Ailort.

This island, locally termed Eilean na Goar, is the most eastern and is bounded on all sides by precipitous gneiss rocks; it is the abode and nesting place of numerous sea birds. The flat surface on the top is 120 feet from the sea level, and the remains of the vitrified fort are situated on this, oblong in form, with a continuous rampart of vitrified wall five feet thick, attached at the SW end to a large upright rock of gneiss. The space enclosed by this wall is 420 feet in circumference and 70 feet in width. The rampart is continuous and about five feet in thickness. At the eastern end is a great mass of wall in situ, vitrified on both sides. In the centre of the enclosed space is a deep depression in which are masses of the vitrified wall strewed about, evidently detached from their original site.

Hamilton naturally asks a few obvious questions about the forts. Were these structures built as a means of defence? Was the vitrification the result of design or accident? How was the vitrification produced?

In this vitrification process, huge blocks of stones have been fused with smaller rubble to form a hard, glassy mass. Explanations for the vitrification are few and far between, and none of them is universally accepted.

One early theory was that these forts are located on ancient volcanoes (or the remains of them) and that the people used molten stone ejected from eruptions to build their settlements.

This idea was replaced 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 dampness of the local climate or the invading armies of the enemy. It is an interesting theory, but one that presents several problems. For starters, there is really no indication that such vitrification actually strengthens the walls of the fortress; rather, it seems to weaken them. In many cases, the walls of the forts seem to have collapsed because of the fires. Also, since the walls of many Scottish forts are only partially vitrified, this would hardly have proved an effective building method.

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. It seemed logical to suggest that perhaps the burning of such a wood-filled wall might create the phenomenon of vitrification.


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.

B BrigantesNation
BrigantesNation May 14, 2002 09:11:32
Replying to BrigantesNation

However, one Scottish archaeologist, Helen Nisbet, believes that the vitrification was not done on purpose by the builders of the forts. In a thorough analysis of rock types used, she reveals that most of the forts were built of stone easily available at the chosen site and not chosen for their property of vitrification.

The vitrification process itself, even if purposely set, is quite a mystery. A team of chemists on Arthur C. Clarke's Mysterious World subjected rock samples from 11 forts to rigorous chemical analysis, and stated that the temperatures needed to produce the vitrification were so intense--up to 1,100°C--that a simple burning of walls with wood interlaced with stone could not have achieved such temperatures.

Nevertheless, experiments carried out in the 1930s by the famous archaeologist V. Gordon Childe and his colleague Wallace Thorneycroft showed that forts could be set on fire and generate enough heat to vitrify the stone. In 1934, these two designed a test wall that was 12 feet long, six feet wide and six feet high, which was built for them at Plean Colliery in Stirlingshire. They used old fireclay bricks for the faces and pit props as timber, and filled the cavity between the walls with small cubes of basalt rubble. They covered the top with turf and then piled about four tons of scrap timber and brushwood against the walls and set fire to them. Because of a snowstorm in progress, a strong wind fanned the blazing mixture of wood and stone so that the inner core did attain some vitrification of the rock.

In June 1937, Childe and Thorneycroft duplicated their test vitrification at the ancient fort of Rahoy, in Argyllshire, using rocks found at the site. Their experiments did not resolve any of the questions surrounding vitrified forts, however, because they had only proven that it was theoretically possible to pile enough wood and brush on top of a mixture of wood and stone to vitrify the mass of stone. One criticism of Childe is that he seems to have used a larger proportion of wood to stone than many historians believe made up the ancient wood and stone fortresses.

An important part of Childe's theory 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.

Critics of the assault theory point out that in order to generate enough heat by a natural fire, the walls would have to have been specially constructed to create the heat necessary. It seems unreasonable to suggest the builders would specifically create forts to be burned or that such a great effort would be made by invaders to create the kind of fire it would take to vitrify the walls--at least with traditional techniques.

One problem with all the many theories is their assumption of a primitive state of culture associated with ancient Scotland. "

Looking at the amount of wood required to vitrify a fort, in addition to the wood contained in the rampart and coupled with the proposal that the process mahes makes the fort stronger. One would have to ask why would an enemy do this?

Therefore, I propose that vitrification was the result of a deliberate act by the builders as part of construction, and was very probably linked with a lengthy religious dedication ceremony and festival.