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A view of the inner fortification of Dún Aonghasa from the cliff edge to the east.

“Mystery” is a problematic term in archaeology, and often linked to the fringes of discourse. For my thoughts on this important caveat, please read the introduction to the first post in this series (about the mystery of Greek Korkyra Melaina in Croatia). There are many mysteries in European archaeology, and they are immensely interesting, but those real mysteries are not necessarily what the “social” media will suggest. The real mysteries and the fake ones are all stories to be told: the real ones open up many new questions and  wider understanding, the fake ones are static. We’re good at real stories and we’re also good at dispelling fake ones.

We have great stories to tell you, about landscapes, about sites, about specific buildings and about individual artefacts in the museums we visit. Often, these stories are answers to the many questions that arise from what is considered a mystery. Sometimes, they are just explanations of why there is no easy answer. In this series, we give you six examples, one from each country we visit, of open questions: in other words, mysteries.

Mystery 3. Ireland: Who built the fort of Dún Aonghasa on Inishmore in the Aran Islands - and why?

Approaching the innermost ring of Dún Aonghasa.

The Aran Islands (Oileáin Árann) are essentially three limestone shelves protruding from Galway Bay off the west coast of Ireland. They have been a much-celebrated spot since the 19th century, noted for their extreme rockiness, for the preservation of a traditional (and very harsh) lifestyle into the early 1900s, and as part of the diminishing areas where the Irish language is spoken in daily life to this day.There is very much to say about the Aran Islands, but for now, let's concentrate on Dún Aonghasa.

Dún Aonghasa (its name is sometimes semi-anglified as Dun Aengus) is the most extraordinary place. A massive and tall semicircular wall of local limestone rubble defines a small piece of flat ground, set on a vertical cliff-edge, 100 metres (330 ft) above the Atlantic Ocean. The drop is beyond sheer: it's an overhang. Visiting the place is in many ways an existential experience: it confronts the visitor with the sheer starkness of how long and inaccessible our own history as a species is and how little we know about it, and with the stark sheerness of this cliff-top place, where you are always a step away from a long and very final drop into the Atlantic breakers at high tide, or onto rock shelves just below the water at low tide.

Above: an aerial view of Inishmore, with Dún Aonghasa in the foregound. The three rings of fortifications and the field of chevaux-de-frise are clearly visible. Image copyright by Chris Hill / Tourism Ireland.

In academic terms, Dún Aonghasa is what we know as a promontory fort. That's a fine set of words, describing a particular site type in Ireland, and usually applying to sites of the "Celtic" Iron Age era, between 1,000 BC and 1,000 AD, the period when Ireland and its offshoots were inhabited and run by Iron Age tribes or clans, local rulerships based on agricultural dependants.

Not a very fertile place: view from the path to Dún Aonghasa.

That's all correct, in a clinical way. I've spent weeks on Inishmore, the largest of the Aran Islands, during my studies and I recommend for anyone to go there to see the islands and to walk their fields. These fields are a testament to what we are, each was achieved by enormous human effort on the part of the hard-worn inhabitants, setting out a field, building walls around it to get rid of the most obstructive bits of rock and to demarcate the plot, usually of very moderate dimensions, then carrying seaweed and sand to make soil in a terrain that had none by itself, to grow poor crops, mainly potatoes (in recent centuries). To walk and understand the fields of Aran is to be in a place like none other. For some, the first visit is a trigger to go there again and spend more time.

Within that experience of rock and walls, Dún Aonghasa is a strange presence. It is evidently built of the same local materials that people have utilised for millennia and it feels, at first sight, to be of similarly human scale. Thus my reference to a "small piece of land" above - it is quite misleading and correct at the same time. A closer look, meaning here a more expansive one, reveals a vast structure, but also - perhaps more pertinently - on entering its inner semicircle, one's entire sense of space changes, as one is now closed off from the familiar scales of the island and its walls, but very open to the vastness of the distant horizon and the ocean far below. The few steps it takes to enter Dún Aonghasa are in themselves a change of perspective. 

The remains of the chevaux-de-frise (northeast section).

So, Dún Aonghasa is at first sight just another set of walls. At second, third and further sights, it is a miracle, forbidding, inspiring and mysterious. There is a massive multi-layer wall laying out a horseshoe enclosure against the abrupt cliff edge, with one narrow entrance. Recently, archaeologists excavated some hut foundations from the Iron age inside the inner fortification. Outside the horseshoe, there is a forbidding jumble of rocks set upright, local limestone broken out of its organic and placid flatness and tilted upright to make a formidable obstacle to anyone approaching the inner ring. Archaeologists call these stones chevaux-de-frise, Frisian horses, referring to a medieval fortification technique aimed at deterring horsemen, but to me, they evoke teeth, an aggressive statement of place, of being inside or outside. On Aran, we are unsure of their purpose and their date and there is an ongoing dispute: such rocks are known to defend forts in Spain in the 2nd millennium BC, but they could also be an Irish phenomenon of the first century AD: after all they are just local slabs of limestone set on edge. One way or the other, the stone field is set off from the surrounding landscape by two more stone walls, more or less concentric with the innermost one. All in all, Dún Aonghasa is huge.

One more view of Dún Aonghasa, sitting in its clifftop perch as it appears to have been doing for about three millennia.

So, how old is it? Unclear, almost certainly Bronze or Iron Age (see below). Who used it or lived there? We have no idea. Is it part of a more general trend? Again, we don't know. What is its purpose? Defence for sure, but against whom? Aran is a small island, did it need such a fort? There are several more stone forts, some quite large, on the islands, so one might be tempted to see Dún Aonghasa simply as part of a very defensive-aggressive medieval landscape. That would make some sense, but it simply does not work archaeologically. A series of radiocarbon dates from the recent excavations are well-attested and the site is definitely much older than the medieval fortified seats of local strongmen it resembles. The dates indicate activity about 3,000 years ago, an era that is the transition between the Bronze Age and Iron Age in Ireland. It is also much more elaborate than other forts. That is actually our main problem with the place: as Aran is small and infertile, there cannot ever have been a large local enemy to justify this enormous fort. There is no usable historic record for any part of Ireland in the first millennium BC and the bits of Irish mythology that survive (they are admittedly copious, but filtered through the Christian tradition of the late first millennium AD) do not refer to Aran or Inishmore in any specifically revealing way. Ancient Ireland, a place of stories, has not left us with a good story for Dún Aonghasa. Instead, we are left with a mystery - and archaeology is the only story we can tell.

Dún Aonghasa may be frustratingly mysterious - or inspiringly so. You can explore it with our expert guides on our Exploring Ireland tour, along with many more mysteries and copious fascinating stories.

If you enjoyed this, also have a look at our other mysteries:

Our Croatian mystery

Our Turkish mystery

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