Header image The Mystery of the Aran Islands and Loch Lurgan

Dúnta Árainn

Tul-tunna ?


      Loch Lurgan

      Dún Aengus

      Dún DubhCathair

      Dún Eócla

      Dún Eoghanachta

      Dún Chonchubhair

      Dún Fearbhaí

      Dún Formna

      Evidence for


      Folklore & mythology



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For hundreds of years the dry stone fortresses, or Dúns (pronounced doons), of the Aran Islands off the west coast of Ireland have intrigued and mystified all who visit them. Historians, archaeologists and experts from the world over, have laboured to explain these mighty Dúns, located on three small Islands in the Atlantice Ocean.

Who built the forts, when were they built and why were they built?

Folklore and historic research have attributed the Dúns to the Firbolg race, amongst others, placing them in late Bronze age. Archaeological evidence to date also links the forts to different periods from Bronze to Iron age to early medieval. Speculation as to their purpose varies from their being defensive forts of one or more chiefdoms to being places of religious rites and customs. In fact all of the above may be true, since I believe the Dúns predate all of these peoples and quite likely have been adopted for various uses.

The purpose of this website is to postulate a completely different reason for the building of the Dúns and as an aside, to speculate on how the cliffs of Aran and the Cliffs of Moher in Co. Clare came into being.  Because of the antiquity of the subject matter, what originally started out as an attempt to explain and understand the Dúns of Aran also attempts an explanation of the development of some of the most spectacular topographical features of the west coast of Ireland. However the main purpose was to consider these ancient Dúns, so many millennia in existence and the reasons they were built. My conclusions about the Cliffs of Moher and the Aran cliffs follow on logically.

As a starting point, I would ask you to speculate on whether Dún Aengus predates the formation of the Cliffs on Inis Mór, the largest of the Aran Islands?   In case you are unfamiliar with Dún Aengus I would point out that it is a massive dry stone semi circluar fortress situated on a cliff top around 80 metres above the Atlantic ocean on Inis Mór, the largest of the Aran Islands. See pictures above. A question often asked is whether this fortress was built as a full circular fortress to be cut in half for some unexplained reason or, as most historians favour, if it was built at the cliff edge as part of a defensive strategy. Whatever your opinion on the matter I invite you to read on and judge the evidence for yourself.

What follows is a story hidden for thousands of years!

The west coast of Ireland circa 10,000 years ago:

To get an understanding of the sequence of events our story must begin at the end of the last ice age approx 10,000 years ago. 

As the ice and glaciers in Northern Europe and North America melted and retreated,  water levels in the Atlantic rose dramatically leading to loss of land around continental shelves and also of islands in the Atlantic, Hy Brazil amongst them, which became inundated and eventually disappeared under the waves.  

Historians have difficulty accepting stories of lost Islands and continents dismissing them as idle fantasies. However stories of lost islands have a curious persistence and remain lodged in folk memories around the world while the islands themselves appear on mariners maps down through the ages until well into the 18th Century when more accurate mapping techniques and exploration confirmed their demise. But one can easily understand the reluctance of the ancient mariners to discard potentially life saving information from the only maps they had.

But back to the story of Aran.  Rising sea-levels caused by melt water is only one part of the story.  A well documented geological phenomenon is that of the earths crust sinking and lifting.  The theory of Isostasy has evolved to explain this phenomenon. The earth’s outer ‘hard’ skin or lithosphere sits on a softer liquid like undermantle, the Athenosphere, that is displaced according to the weight of the land mass above it. (Think of jumping onto a water bed, where the skin of the bed is the earth’s crust). When kilometre high glaciers load the land, the weight of it causes the crust underneath the ice to sink into the softer Athenosphere.  Then when the ice melts the land underneath lifts back, quickly at first and then more slowly at a rate of cm s per year for hundreds of years.  Eventually the land will reach its equilibrium level and stop rising.  The whole cycle repeats itself again and again as it has done many times in the past with each successive ice age.

Therefore in the Ireland of 10,000 years ago, two things happened that affected sea-levels: Water volume increased rapidly and the 'unloaded' landmasses began to lift.  While the water rose rapidly, it is difficult to say how quickly the land lifted but most likely it lagged the rising tide by a few hundred years.  Studies have shown that the ‘bounce back’ effect to be exponential in its effect with most of the bounce coming in the first 4-5 thousand years.   Bear in mind also that land further out in the Atlantic that was not loaded by icesheets or glaciers would not rebound as it was already at equilibrium level.  In fact as it became inundated it would sink further.  People living at these times would have noticed significant water level increases – several inches a year – which, after a generation or two, would have caused land to be inundated and abandoned, especially if the rate of sea level rise attributable to melt water was greater than the rate of land ‘bounce back’.

Another point to remember is that water also has weight and causes land below it to sink just like an ice sheet. In this case the Isostasy is calle Hydro-Isostasy. It follows therefore, that land under a deep ocean will not rise as much as land under shallow water. The greater the inundation the greater the loading and the greater the submergence. Just like a ship sinking once land goes under it is unlikely to lift back unless Eustatic water levels reduce at a rate faster than the land sinks, allowing the land to break above water again and start to lift.

Try to imagine yourself as a coastal dweller around the Irish coast 7,8 or 9 thousand years ago. The interior of the island was densely forested following the disappearance  of the ice sheet in the previous millennium.  People were only starting to clear the forests and plains and lived mainly on the coasts.  Ireland was still connected to Britain and Europe as water levels were low and had not breached the land bridges.The coast of Western Ireland extended up to 10 or 20 miles beyond where the Aran Islands are located today. The melting of the ice sheets of North America and Northern Europe increase the volume of water in the oceans leading to increased tidal instability and inundation.

The rising sea threatens everyone and refugees from inundated lands arrive along the coasts forcing people to clear forests create plains and move inland. These people had a tradition of sea defence, they built Dúns to defend themselves from the rising sea and from Tsunami, with which they were intimately acquainted.  The more experience they got the bigger they built. First one wall, then a second supported by the first but higher, then a third wall supported by the second but higher again and even a fourth wall supported by the third but higher still.  The effect from the inside of the Dúns is one of terraces leading from one wall to the next. But the terraces were in fact a side effect of the construction. These forts could have been up to 10 metres high and at least 7 metres in dept.  To build one cicular wall of that height on it’s own would have been useless in the face of Tsunami. Experience had thought them that.

The building of these forts was most likely done at a time of low 'relative sea-levels', before the land of the Burren and Aran had experienced significant isostatic lift or glacial rebound.  The Aran islands were not yet islands and were still joined to the Burren on the coast of Clare. This was at a time prior to the formation of the Cliffs of Moher and the cliffs of Aran when, significantly for the forts today, there was land to the south and west of the islands.  Assuming they were built as Tsunami defences, all the forts were completely enclosed circular forts and not ‘half’ forts situated on cliff tops as Dún Aengus and Dubh Cathair are today. There were no cliffs where we have them today, just low lying land threatened by meltwater and rising sealevels. Loch Lurgan was a lake,as its name in Irish still suggests and Galway Bay, it's name in English was a long way into the future!

The sea kept rising.  People built sea defences, not just on Aran, but on the Burren and up and down the coast of Ireland from Steague Fort in Co. Kerry to An Grianán in Donegal.  No doubt some lost the battle and land was abandoned.  The Irish coastline at that time, as we know it today was inundated since it was still depressed from the ice sheets at a time when sea-levels were much higher. The land that was to become the Aran Islands was inundated like Hy Brazil. However, since it survives today, it is probable that it was only lightly inundated by a few meters of water which retracted later due to glacial rebound and other events explained below.

Refugees moved deeper into the Burren in Co Clare, building more forts to stop the ever rising sea.  The high land of the stony coast of Co Clare has many ancient stone forts testifying to the sea battles of those early coastal dwellers.  The fort of Ballykinvarga in Co Clare inerestingly has a 'Chevaux de Frise' feature that is similar to the Aran Island forts of Dún Aengus and Dubh Cathair thus linking all these forts to a common purpose.

So what happened in the end?  Do we know who won and who lost? This is open to debate and awaits further research to complete the story.  However, here is my opinion of what may have happened:

Relative sea-levles reduced dramatically due to the compound effect of the four phenomenon: 1- Hydro-isostasy; isostasy caused by weigth of water act like ice-sheets to depress the ocean basins, causing a reduction of sea-levels on associated coasts, 2 – the volume of melt water reduced dramatically with the stabilisation of the ice sheets, 3-  the sea broke into new valleys such as the Irish Sea, North Sea and Mediterranean Sea, causing the separation of Ireland and Britain from each other and from the Continent, and at the same time acting as a valve to reduce sea levels  and 4 – the landmass of Ireland and northern Europe bounced back at an accelerated rate. Before long - maybe a couple of thousand years! – people in Co. Clare and the coasts could not conceive of the sea being a problem. In fact as the land kept rising more coastline was recovered from the sea!

And the land of Aran reappeared, but this time as three islands separate from the coast of Clare with cliffs at their back.   Simultaneously, as the seas receded the Cliffs of Moher and the cliffs south of Aran lifted into prominence.  As the land continued to lift the cliffs became even higher in a process that happened over thousands of years.  This process went unnoticed by the humans living there.  What they did notice was that the sea was no longer a threat!  The forts built as a defence against sea were put to new uses. 

Very soon people forgot why the forts were built, in fact, if they were told the reason, they would never have believed it since the sea was now hundreds of metres below the coast!

How were the Cliffs of Moher and Aran created?

The creation of the cliffs of Aran and Moher was, I believe, created principally by the lifting of the landmass of Aran and the Burren ,  via a normal isostatic response which occurred for a few thousand years after the ice age. The adjoining continental shelf that existed at the south of the Islands at the time of the building of the Dúns and the seabed that make up the sounds between the Clare and Inis Oir and in between the three Aran islands did not lift, resulting in the creation of the islands, the formation of the cliffs and, most tellingly, the severing of the ancient sea defence forts of Dún Aengus and Dubh Cathair. 

The rebound of the land was probably accentuated by the depression of the inundated land due to Hydro-isostasy and it may be that the combinded effect was what led to the creation of these spectacular cliffs. A documented effect of Isostasy is to create a 'forebulge' outside the margins of the ice-sheet where land, geologically linked to land under the ice-sheet is lifted up as the other end of it is depressed by the ice in a kind of see-saw effect. Therefore coasts in the forebulge area beyond the edge of an ice sheet are candidates for inundation as this see-saw effect reverses. It is conceivable that land in the forebulge area would break away depending on the amount of isostatic lift on the adjoining area. This gives us a plausible explanation for the faultline along which the cliffs of Moher and Aran appeared.

The lifting of the land and the creation of the cliffs probably started at a time of high sea levels.  i.e. the process started under the sea unseen by human eyes.  By the time the land had lifted sufficiently and the sea-levels reduced, the cliffs of Moher and Aran were already at a significant height.   The increase in cliff height continued at a snails pace unnoticed by ordinary people who would have attributed it to the lowering of the sea.

The storm beaches above the cliffs of Inis Meain and Inis Mór are evidence of high relative sealevels at a time prior to isostatic rebound and / or forebulge depression.

This brings me to the end of the story of why the Dúns of Aran were built and how the cliffs of Aran and the Cliffs of Moher were created!

Fantastic stuff, I hear you say and much too incredible to be true! Perhaps, but I leave that to the experts to decide. If nothing else I hope the theory will provoke debate and stimulate imaginaton that will lead to fresh insights and discoveries regarding the origin and purpose of these Dúns and other monuments from our ancient past.

So where is the evidence?

Naturally people will ask where is the evidence?   The supporting facts for this theory lie in the Dúns of Aran themselves, the storm beaches and Connemara granite boulders strewn on clifftops, the shellfish 'midden' deposits and other corroborating facts that I shall outline below.

The foundation of the argument rests completely on the presumption that the Dúns were built as Tsunami shelters. This is the major hurdle that has to be proven if this thory is to have any valididity.  If we can prove this point, or disprove it, the argument will stand or fall accordingly. Rising sea-levels of their own do not necessitate building these shelters as people would have slowly migrated to higher land to escape creeping inundation over generations. The existence of Tsunami Shelters, however, carries much greater significance. To have built forts specifically for this purpose implies a knowlege and familiarity with earthquake waves unparalleled even by todays standards. These people were of a race that knew earthquakes and the earthquake wave. They built their forts to the best standards of their time. Circular forts with three or four walls rising one against the other and each higher than the other. All the forts contained internal Clochans or stone huts to protect the inhabitants from falling debris and perhaps store boats. The external chevaux de frise was a mechanism to deflect the power of the Tsunami wave and minimise the impact on the walls.

The question as to why there were so many earthquake waves seven,eight or nine thousand years ago begs an answer assuming these forts were Tsunami shelters. Therfore before attempting this we must first try and prove that the purpose of the forts were as Tsunami shelters.

In support of the argument, on the next page I outline a summary of the evidence ‘for’ the Dúns of Aran being TSUNAMI shelters.

Next page - the evidence!