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Vitrified Forts? (Scottish Hill Forts; Inca Structures, Etc.)

Fascinating stuff!

A laser isn't the only thing that could do something like that. A plasma cutter or a thermic lance might be able to do it. If the Incas had found a way to produce a high temperature gas or thermic reaction, they may have been able to do this.
However, no evidence of this ancient technology exists, so we'll never know.

Thermic lance demo here:

http://www.youtube.com/watch?v=EV4r7OKkXmU

Using this, I don't think you could achieve the kind of precision seen in those photos.
 
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Mythopoeika said:
Fascinating stuff!

A laser isn't the only thing that could do something like that. A plasma cutter or a thermic lance might be able to do it. If the Incas had found a way to produce a high temperature gas or thermic reaction, they may have been able to do this.
However, no evidence of this ancient technology exists, so we'll never know.

Thermic lance demo here:

http://www.youtube.com/watch?v=EV4r7OKkXmU

Using this, I don't think you could achieve the kind of precision seen in those photos.
Great insight Mythopoeika! They could have managed something like that, but as you say, until more evidence is found --a smoking lance, as it were...
 
That is a real eye-opener.
Stone engineering must have reached its height back then, never matched since.

Reminds me a bit of Roman concrete, which has proved to have a longevity not matched by modern concrete.
 
It doesn't surprise me that techniques that were known to prehistoric peoples get lost. We are in the process of doing the same thing ourselves, in our case mainly because newer , quicker, cheaper, technologies have replaced them.

Currently, there are written records which will help us recreate the technology if we need it. In 100 years that may not be the case - if you have your records stored on, say, floppy disks you are going to have a heck of a time recovering them.
 
There's apparently the remains of a vitrified fort at Sainte-Suzanne, Mayenne, not far from where my wife's family live. Next time we're over in France, I will explore the ruins and post some pictures here.
 
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Is there a possibility that these structures became vitrified, via another process? That is; instead of extreme heat, which is often stated as the cause, rather; extremely cold and rapidly cooling temperatures, which can also cause vitrification of an amorphous solid. As far as I can make out, and I'm no expert; gases emitted by rocks can, firstly, transform to a liquid medium and as they cool, then become an amorphous structure and then; glass. These processes occur at a molecular level.
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As I say, I'm no expert on these matters, so if I have this wrong, then I hold my hands up.
Is there someone on the board who can elaborate on this process and prove me right, or wrong, whatever the case?
 
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I will be driving through France over the Easter break and will try to do a detour to Sainte-Suzanne (between Laval and Le Mans) to have a look at the mysterious vitrified walls. Hope to post some photos here on my return.
 
Still in rural France for a couple more days and mostly off-grid, but visited Sainte-Suzanne yesterday and will post photos of the curious vitrified stone when I get back.
Happy Easter fellow Forteans!

Glad to hear that you weren't abducted by any Aliens still hanging around the forts!
 
Got home late last night and, as promised, here's my Fortean field report from Sainte-Suzanne.

First, I should state that my expectations were perhaps unrealistically high. When I heard about "les murs vitrifiés", I envisioned seeing a whole swathe of wall turned to glass. The reality was somewhat different.
Taking a 25km detour from my route through rural Mayenne, it was a very pleasant drive along remarkably straight, tree-lined roads, with hardly any other vehicles in sight (I always enjoy driving in countries less overcrowded than Britain). Sainte-Suzanne is an achingly beautiful village, dominate by the still imposing ruins of an 11th century castle and a later, round-turreted Chateau. Parking my Jeep in the village square, I walked up the hill, past the enticing cafés and antique/curiosity shop to the tourist information centre. I asked the attendant about the vitrified walls and she gave me a map, pointing out their location, to the south of the recommended walking trail around the village. As an aside, whilst my French is quite good, I was delighted that she thought I was French and asked which départment I hailed from! Anyway, off on my hike and the first thing I noticed was that several labyrinthine village streets are marked by large Tarot-card signs - how delightfully Fortean! So, I reached the southern end of the trail and turned to my left, passing a crumbling medieval tower and approaching the spot where my map urged me not to miss the vitrifications. Well I looked. And looked. And was initially underwhelmed. I then realised that there were chunks of shiny, almost black, obsidian-like stone, embedded in the dry-stone walls and in the tall ramparts themselves. So, this was not some prehistoric wall, mysteriously turned into a glass-like state, but more to do with opportunistic 11th century construction workers finding the area strewn with strangely glass-like blocks and embedding them in the castle walls. The size of the blocks varied from similar to a modern household brick, up to rough cubes around 30cm/1ft square. Sadly there was no explanation given either on my information pamphlet or on the website as to why there was a proliferation of vitrified blocks in the area. Snapped a few shots and then stopped for a well-earned beer before heading back to my in-laws house for a substantial dinner.
A few photos below:

sainte_suzanne6.jpg
sainte_suzanne1.jpg
sainte_suzanne3.jpg
sainte_suzanne4.jpg
sainte_suzanne2.jpg sainte_suzanne5.jpg
 
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What's the current state of knowledge on vitrified hill forts?
Has the method ever been duplicated in modern times, or is it a lost art?

Skeptoid had this to say about vitrified forts:
https://skeptoid.com/episodes/4326

There have been various theories put about as to why the vitrification was done. The first being that it was a result of accidental fire. Given that a stone wall is a large investment in time, and ancient cultures had a tendency, archaeologically speaking, towards rebuilding on the same site of previous habitation, commonly using the Hebrew word "Tel" to denote a settlement built on the rubble mound of a previous settlement. Now as this is likely to occur whether a settlement is destroyed by accidental or deliberate fire, the more likely answer is that it was a deliberate effort. No doubt people had observed that stone can melt during the process of smelting for ore, and sought to replicate that process for wall building rather than investing in expensive lime mortar, or having no mortar at all. No doubt it would involve burying the wall before firing it, as the heat would need to be concentrated as in a kiln or a charcoal burn. That is possibly why many of the walls were found buried; I suspect the process was abandoned as not being very successful, given that glass is generally weaker than normal stone, and there isn't much evidence to suggest that the bonding worked reliably.
 
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As with so many Fortean subjects, the common reaction to the mystery is often as fascinating as the mystery itself.

When you read about vitrified forts, you could be forgiven for imagining walls that had been fused into a single continuous, rather lumpy piece of glass with the shapes of the original rocks being barely discernible. How could this be caused by anything less than lasers, or a nuclear attack? How indeed?

However, a bit of simple searching shows that the vitrification was patchy, ranging from entire lengths of wall to isolated sections, small groups of rocks, and so on. Sometimes, rocks are fused together and at other times, only glazed or partially melted.

The four causes to consider are:

1) Extreme natural causes, such as comet strikes. This can be excluded simply because there are so many examples, so widely dispersed. What natural cause could be so extreme, and so comparatively common (over 100 instances) and yet not obvious to us? What natural cause would only occur over a period of a few centuries? Where are the vitrified ancient Greek, or Roman, high mediaeval, or Tudor structures, for example? What natural cause would only affect built structures but not the scattered natural rocks in the same area? No, we can reasonably exclude this.

2) Accidents, such as accidental fires. Many of the same considerations apply. Why did they only have such accidents in such a small window of time and place?

3) Deliberate enemy action in an attack. This could be subdivided into (3a) rival tribes using conventional iron age/early mediaeval techniques, and (3b) some previously unknown technological superpower.

3a) Rival tribes. There would be no obvious advantage in vitrifying an enemy's fort in the course of an attack. In iron age and early mediaeval times, long sieges were probably rare because of the logistical problems and the the absence of standing armies. If a fort were to be attacked at all then subterfuge or direct assault would be likely, and any use of fire would probably be focussed either in the area of the intended assault, or in one other place as a distraction. Piling wood, brush or peat, or similar combustible substances against the wall would be difficult if the defenders were armed with slings, arrows or javelins. It seems unlikely.

3b) Unknown technological superpower (including space aliens). Firstly: why use atom bombs or lasers on a primitive garrison of iron age fort dwellers? If you can make atom bombs or lasers, you can probably make helicopter gun ships, machine guns, armoured fighting vehicles, mortars, or any of a hundred other comparatively simple pieces of hardware that would do the job more efficiently. Lasers famously fire in straight lines, so why use them to fuse the defences, rather than picking off individual guards or key timber buildings? Finally, where is the other evidence of this technological superpower? Where are their own buildings, their roads, their artefacts? As Sagan said, extraordinary claims require extraordinary evidence, and as Occam's razor instructs us, why make these extra assumptions rather than working with the evidence we already have? I think all these "unknown superpower" explanations should be dismissed until we have a credible case for a particular technological superpower having existed at the time.

4) Deliberate act for cultural reasons. This could break down into (4a) by the constructors, and (4b) by victorious enemies.

Whichever version of (4) we consider, the explanation has to lie in this general area. The phenomenon is comparatively limited geographically (primarily Scotland, but also some other parts of Britain and western Europe) and is also limited in terms of period: iron age and early mediaeval — or, as we used to say, "the dark ages".

So there was something cultural going on in that region in that period.

People have been sceptical about it being for defensive purposes because vitrification "weakens the rock". However, in that period, no one was using artillery to smash the rock. Any attempt to breach the walls would probably be by digging at them, and rocks that are bonded together would be harder to remove than loosely piled dry stone walling. However, I favour the idea that if a fort were to be attacked, it would probably be either by subterfuge or by direct assault, rather than siegecraft.

We could of course hide behind the archaeologist's traditional catch all of "ritual significance". The vitrification could have been to sanctify the fort, or purge it of spirits, or to cleanse it, or to neutralise it at the end of its useful life. We have examples of other old structures that were systematically destroyed, or filled in, as if the intention was to dispel something: memories, associations, evil spirits?

A simpler explanation may simply be status and aesthetics. When we see hill forts today, we see misshapen banks and ditches and rocky or grassy enclosures. These once thriving places are now often bleak. In use, the banks and ditches may well have been well kept, and perhaps faced with timbers or stones, maybe whitewashed, or deliberately blackened with soot. Perhaps thorny plants such as gorse were encouraged to grow in the ditches or on the outside faces of the banks as a natural way of slowing down attackers — with the additional benefit of gorse flowers being attractive. The banks may well have had timber palisades and maybe even lengths of timber rampart, isolated watch towers, and a timber gate house straddling the main entrance. Any and all of these may have been decorated with banners, coloured or painted hides, and so on. Against this background, partial vitrification of the stones to create a particular visual effect may have been no more than a fashionable statement of power and prestige.

I am no expert, but reading on the subject tells me that temperatures of 1,200 degrees would have been sufficient to vitrify some of the rock. Iron oxide can produce iron at 1,250 degrees, so in the iron age, they at least had the capability to produce temperatures this high. After that, it becomes merely a question of scale, determination and technique.

While we sit at our desks wondering how "the ancients" built Stonehenge, or Avebury, or the pyramids, or the vitrified forts, without modern technology, they just got on with it. If you have enough people, enough time, enough will to succeed, and a strong leader with access to the skills, then no special technology is required.
 
I am no expert, but reading on the subject tells me that temperatures of 1,200 degrees would have been sufficient to vitrify some of the rock. Iron oxide can produce iron at 1,250 degrees, so in the iron age, they at least had the capability to produce temperatures this high. After that, it becomes merely a question of scale, determination and technique.
I wonder whether the stones were originally built using a poor clay as a mortar and they were then fired to set the clay. In the couple of thousand years since, the clay has long since eroded away leaving a few patches of vitrified rock.
 
Unfortunately I can't remember where I read this, but someone has postulated that the source of the heat which vitrified the forts was an array of mirrors concentrating the sun's heat in the same way that Aristotle is said to have burned Roman ships at the siege of Syracuse. At least some of the reenactments of this event worked, so it would have been possible to raise the appropriate degree of heat.
I imagine an army with each soldier having a polished bronze shield and all of them striving to get their individual reflections of the Sun onto one spot, possibly the ramparts, trying to burn individual defenders, or on to weak spots in the fort's walls.
 
Did they have magnifying glass technology in those days? Is that worth considering?
 
Got home late last night and, as promised, here's my Fortean field report from Sainte-Suzanne.

First, I should state that my expectations were perhaps unrealistically high. When I heard about "les murs vitrifiés", I envisioned seeing a whole swathe of wall turned to glass. The reality was somewhat different.
Taking a 25km detour from my route through rural Mayenne, it was a very pleasant drive along remarkably straight, tree-lined roads, with hardly any other vehicles in sight (I always enjoy driving in countries less overcrowded than Britain). Sainte-Suzanne is an achingly beautiful village, dominate by the still imposing ruins of an 11th century castle and a later, round-turreted Chateau. Parking my Jeep in the village square, I walked up the hill, past the enticing cafés and antique/curiosity shop to the tourist information centre. I asked the attendant about the vitrified walls and she gave me a map, pointing out their location, to the south of the recommended walking trail around the village. As an aside, whilst my French is quite good, I was delighted that she thought I was French and asked which départment I hailed from! Anyway, off on my hike and the first thing I noticed was that several labyrinthine village streets are marked by large Tarot-card signs - how delightfully Fortean! So, I reached the southern end of the trail and turned to my left, passing a crumbling medieval tower and approaching the spot where my map urged me not to miss the vitrifications. Well I looked. And looked. And was initially underwhelmed. I then realised that there were chunks of shiny, almost black, obsidian-like stone, embedded in the dry-stone walls and in the tall ramparts themselves. So, this was not some prehistoric wall, mysteriously turned into a glass-like state, but more to do with opportunistic 11th century construction workers finding the area strewn with strangely glass-like blocks and embedding them in the castle walls. The size of the blocks varied from similar to a modern household brick, up to rough cubes around 30cm/1ft square. Sadly there was no explanation given either on my information pamphlet or on the website as to why there was a proliferation of vitrified blocks in the area. Snapped a few shots and then stopped for a well-earned beer before heading back to my in-laws house for a substantial dinner.
A few photos below:

View attachment 9088
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View attachment 9093 View attachment 9094

Slightly off-topic, but the village of Sainte-Suzanne has its own artisanal brewery, which supplies local shops with, traditional, unfiltered, bottle-conditioned beers. On my last visit last month, I treated myself to a boxed set of their delicious beers. Finished the last bottle yesterday a dark 5% stout (and wish I'd brought some more back now). The beer labels feature some striking artwork with Fortean themes.
This is the label for the 8% Abbey-style beer:

IMG_0513.JPG

http://www.brasserie-la-suzannaise.fr/actualites.html
 
Slightly off-topic, but the village of Sainte-Suzanne has its own artisanal brewery, which supplies local shops with, traditional, unfiltered, bottle-conditioned beers. On my last visit last month, I treated myself to a boxed set of their delicious beers. Finished the last bottle yesterday a dark 5% stout (and wish I'd brought some more back now). The beer labels feature some striking artwork with Fortean themes.
This is the label for the 8% Abbey-style beer:

View attachment 12536

http://www.brasserie-la-suzannaise.fr/actualites.html

As we're currently in Mayenne, was planning to drive to Sainte-Suzanne today and take in a trip to the brewery. Sadly, my brother-in-law has informed me that the master brewer has died and La Suzannaise artisanal micro-brewery closed this year.
Still, we have the vitrified stones of the fortress ruins to enjoy and perhaps a café or two.
 
Slightly off-topic, but the village of Sainte-Suzanne has its own artisanal brewery, which supplies local shops with, traditional, unfiltered, bottle-conditioned beers. On my last visit last month, I treated myself to a boxed set of their delicious beers. Finished the last bottle yesterday a dark 5% stout (and wish I'd brought some more back now). The beer labels feature some striking artwork with Fortean themes.
This is the label for the 8% Abbey-style beer:

View attachment 12536

http://www.brasserie-la-suzannaise.fr/actualites.html
H'mmm you need a brew with more body - try Betty Stogs
Betty Stogs.png
 
Wasn't able to upload the pic yesterday, as it was too big for my roaming data limit. On Brittany Ferries WIFI now, so here's the photo I took yesterday of some black vitrified stones at Sainte-Suzanne :

PSX_20190228_080137.jpg
 
Wasn't there an experiment done with using brushwood loosely packed being able to generate the necessary temperatures?

Ah, yes! THE EXPERIMENTAL PRODUCTION OF THE PHENOMENA DISTINCTIVE OF VITRIFIED FORTS. BY PROFESSOR V. G. CHILDE AND WALLACE THORNEYCROFT, in 1937 found via Skeptoid

Interesting point is that in various places in Cornwall (and probably elsewhere) there is plenty of vitrified stone used as building material but it is the product of breaking down tin roasting furnaces and (round Hayle) foundry detritus. Of course, all these are far more modern than the hill forts
 
It's my understanding that extreme heat will weaken individual stone blocks, but can greatly strengthen the mortar holding it together. And, although it weakens stone, I believe that exposure to very high temperatures will - at least in the case of certain types of rock - decrease its porosity*. Looked at independently of other factors those latter elements might suggest a deliberate part of the structural process, designed to increase stability and weatherproofing, rather than for conflict related reasons (as fearsome as the locals were back then - I suspect wind and rain were a much more constant form of savagery.)

However:

...When you read about vitrified forts, you could be forgiven for imagining walls that had been fused into a single continuous, rather lumpy piece of glass with the shapes of the original rocks being barely discernible. How could this be caused by anything less than lasers, or a nuclear attack? How indeed?

However, a bit of simple searching shows that the vitrification was patchy, ranging from entire lengths of wall to isolated sections, small groups of rocks, and so on. Sometimes, rocks are fused together and at other times, only glazed or partially melted...

...there's the rub.

Seems to me that the patchiness of the process undermines, to a certain extent, many of the explanations offered (especially, maybe, the more extreme).

Another thing I've often wondered: the extreme temperatures needed to fuse stone would surely leave other evidence at the burn site. Has anyone ever studied soil samples at the sites - would evidence not show up here?

As with so many Fortean subjects, the common reaction to the mystery is often as fascinating as the mystery itself...

Oh, yes. One of the reasons I find Forteana so fascinating is that, very often, even if there's maybe nothing going on, there's still something going on. (A good example of this might be Gareth William's book A Monstrous Commotion. You do not have to believe in the Loch Ness Monster at all to find the subject - it's history, the way it has unfolded into our collective consciousness, the characters involved and their often conflicting theories - absolutely fascinating.)

*I have seen these factors in relation to experiments made at a site not so far from where I am now, but can't recall other details, or find a source just now - I'll keep scratching my head.

Edit: So I misunderstood the porosity issue. Apparently solid sandstone increases in porosity, but this decreases in powdered sandstone - quite dramatically. This was found in experiments made in realtion to Wincobank in the Sheffield area. I've read this in a paper publication somewhere - but there's a reference to it in a National Geographic article here. I had it in mind that this experiment had been made in relation to Carl Wark, which is just up the road from me but which I don't think has any evidence of vitrification (although, actually, it does have a slightly mysterious wall); so much for my memory
 
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...Interesting point is that in various places in Cornwall (and probably elsewhere) there is plenty of vitrified stone used as building material but it is the product of breaking down tin roasting furnaces and (round Hayle) foundry detritus. Of course, all these are far more modern than the hill forts

Yes, another factor I wondered about. Worked stone was a valuable asset (always has been, and still is, for that matter) - I wondered if stone from redundant metal working areas might have been recycled into the wall building. I suspect though that there simply wouldn't be enough of this to explain away the extent of the evidence. It also wouldn't explain the fusing of mortar in the walls.
 
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Dragon attack! Mystery solved.

I haven't read any explanation that satisfactorily explains both the how and the why of this mystery. One or the other, but not both. The feeling that some piece of evidence or obvious idea is missing is strong for me.
 
Yes, another factor I wondered about. Worked stone was a valuable asset (always has been, and still is, for that matter) - I wondered if stone from redundant metal working areas might have been recycled into the wall building. I suspect though that there simply wouldn't be enough of this to explain away the extent of the evidence. It also wouldn't explain the fusing of mortar in the walls.
For myself, the question is not so much "how" but "why"

The traditional answer seems to be that, where there was mortar in the walls it strengthened that or possibly made it less porous as the heating does not strengthen the stone. My idea is to ask what colour these walls would have appeared at the time? I suspect that it would have been dead black making these structures far more apparent in the landscape.
 
You do not have to believe in the Loch Ness Monster at all to find the subject - it's history, the way it has unfolded into our collective consciousness, the characters involved and their often conflicting theories - absolutely fascinating.)
Yes, quite so.
 
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