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Thursday, 12 May 2011

The Miracle of Barnenez


Never had an opportunity to visit this one in Brittany.  But it has to be one of the Wonders of the World.  Look at the sheer scale of it -- in many ways it is more impressive than Silbury Hill, Stonehenge, Avebury and Carnac.  The engineering skills involved are mightily impressive, and show that between 7,000 and 6,000 years ago the Neolithic people in this area knew how to use corbelled vaulting techniques to make their chambered tombs.  Later they were called "beehive cells or tombs" -- and in Greece the word "thalos" is also used.  Nine of the eleven chambers have corbelled vaulting in them -- and in two the corbelling technique was used from the ground up.  I think that's cleverer than putting up big stones and placing lintels on top of them........

And these guys had also worked out how to make something that is essentially a stepped pyramid...... more than 6,000 years ago.  

From the Wikipedia entry:


The Cairn of Barnenez  is a Neolithic monument located near Plouezoc'h, on the Kernéléhen peninsula in northern Finistère, Brittany (France). It dates to the early Neolithic, about 4500 BC; it is considered one of the earliest megalithic monuments in Europe. It is also remarkable for the presence of megalithic art.

Radiocarbon dates indicate that the first phase of the monument was erected between 4850 and 4250 BC, and the second phase between 4450 and 4000 BC.

Secondary use
Pottery found in and around the monument indicates that it underwent a period of reuse in the Bronze Age, in the 3rd millennium BC.

Recognition as an ancient monument
The cairn was first mapped in 1807, in the context of the Napoleonic cadaster. Its first scientific recognition took place in the context of an academic congress in Morlaix in 1850, when it was classified as a tumulus.

Quarry damage
Privately owned until the 1950s, the cairn was used as a quarry for paving stones. This activity, which threatened to destroy the monument, was only halted after the discovery of several of its chambers in the 1950s. The local community then took control of the site.

Restoration and excavation
The cairn was restored between 1954 and 1968. At the same time, vegetation was removed from the mound and systematic excavation took place in and around the monument.

The monument

Today, the Barnenez cairn is a 72 m long, up to 25 m wide and over 8 m high. It is built of 13,000 to 14,000 tons of stone. It contains 11 chambers entered by separate passages. The mound has steep facades and a stepped profile. Several internal walls either represent earlier facades or served the stability of the structure. The cairn consists of relatively small blocks of stone, with only the chambers being truly megalithic in character. The monument overlooks the Bay of Morlaix, probably a fertile coastal plain at the time of its erection.

The monument is the result of at least two phases of building.

Cairn 1, before 4,500 BC
In a first phase, a slightly trapezoidal mound of 32 m by 9 to 13 m was erected. It contained 5 chambers and was surrounded by a double kerb. The first phase favoured the use of dolerite.

Cairn 2, circa 4,200 - 3,900 BC (?)
In a second phase, an extension with six further chambers was added in the west. At the same time, Cairn 1 was enveloped in a wider and taller structure; its passages had to be extended. More granite was used in this phase.



The chambers
The 11 chambers of the Barnenez cairn are of the type known as Dolmen à couloir in French archaeological terminology. The term translates roughly as "passage grave". They are built of large slabs of slate and granite. Originally, all the chambers were entirely enclosed by the mound. The fact that several of them are partially exposed now is the result of modern quarrying.

Each of the 11 chambers is reached from the southeast via a long narrow passage (7–12 m long). They are arranged parallel to each other. Shapes and construction techniques differ slightly.

In nine cases, narrow passages lead to corbelled chambers. Normally, the corbel vault rests on orthostats, in one chamber it actually sits on the ground, forming a true tholos. The passages have slab-built or dry stone walls and are covered with slabs. One of the chambers has a dry-stone vaulted ante-chamber.

One cubic meter of the Barnenez cairn contains 1,500 kg of stone. It is estimated that the quarrying, fashioning, transport and construction of such an amount represents about four work days for a single worker (assuming a 10-hour day). The original monument, Cairn 1, had a volume of about 2,000 cubic metres; it is built of 1,000 tons of granite and 3,000 tons of dolerite. It would thus have required 15,000 to 20,000 working days; in other words, it would have taken 200 workers three months to erect Cairn 1 alone. In its final form, the Barnenez mound is nearly three times as big as the first phase.

Engraved symbols occur in several of the chambers and passages. They depict bows, axes, wave symbols or snakes and a repeated U-shaped sign. One of the carved slabs is in secondary use was originally part of a different structure, an interesting parallel to the situation in several other such monuments, including Gavrinis. The symbols on the engraved blocks resemble those found in other megalithic monuments in Brittany; in broader terms they belong to the cultural phenomenon described as megalithic art. One of the recurring symbols is sometimes interpreted as an anthropomorphic depiction (the so-called "Dolmen Goddess").

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There's an interesting article here:
http://findarticles.com/p/articles/mi_hb3284/is_n257_v67/ai_n28633156/?tag=content;col1
Antiquity / Dec, 1993

New radiocarbon dates from Bougon and the chronology of French passage-graves

by Chris Scarre, Roy Switsur, Jean-Pierre Mohen 

The authors argue that these Neolithic structures may be among the earliest major structures in the world -- and they are certainly more than 2,000 years older than the earliest Egyptian pyramid.

3 comments:

Tony Hinchliffe said...

When you went on your twinning trip, Brian, organised between Plouguin, Brittany, and your home terrain in Pembrokeshire, did you come away with any impressions (perhaps from discussions with your French hosts) that there were any meaningful prehistoric cultural and trade links between Brittany and South West Wales?

Constantinos Ragazas said...

Brian,

This is very impressive indeed! I am truly intrigued and somewhat perplexed. It reminds me a little of some Central American monuments. Some questions.

1) Is this entire structure man-made out of stone? Or made using existing natural formations
2) Does it have foundations?
3) Why are its walls, contours and terraces so irregular? Wont it make sense that if men could built such immense structures out of stone, they could also do it in straight and rectangular design? Or in the original structure it was so?
4) Are the dates obtained from radiocarbon dating of organic material found inside the chambers only?
5) Could the chambers have been added at a later date?
6) Any engineering studies made on the structure and the corbel vaulted chambers that could explain how such a structure could have lasted for 6500 or more years?
7) The photo of some corbel vault that you took in an earlier post shows a ceiling made of stones but does not look exactly as being corbel in structure. I think I could actually trace whole stones in the ceiling which were not really fixed in place by overlaying stones keeping them down. I could be wrong in this, since the picture was not very clear. How I wish I was there to examine these!
8) Is it known from where exactly all the stones were quarried? Or all these small stones were found in the surrounding land.

OK. Enough questions! Any answers?

Kostas

BRIAN JOHN said...

Hello Kostas. Lots of questions which I'm not qualified to answer. I refer you to the Wikipedia entry on Barnenez and the work of Chris Scarre and others. Plenty available on the web! My impression (not having visited the site) is that the structure is entirely man-made, mostly with quite small stones, with all the chambers built as the work progressed in two phases. It looks pretty regular to me -- given that the ravages of time, over more than 6,000 years, have inevitably caused some section s of the facade and other parts of the structure to collapse. The quarrying did immense damage until it was stopped in the 1950's.

As for the corbel vaulting, I can conform from Ile Carn that this is proper corbelling, with each flattish stone partly overlapping the stones below, and then overlapped itself by the stones above. Very clever indeed.