Archaeology Orkney

Well we have reached the end of the excavation season at The Cairns. Let’s review what we set out to do and what was achieved.

Birth of a broch: the southwest extension

We extended the main trench on the south-western side of the broch this season. This was quite a large new area, and I must confess that the intention here was that we would not necessarily do a great deal of work in this area this year. I wanted to get a better more expansive view of the southern arc of the broch wall and possibly see hints of the extramural complex of buildings. However, from the outset the deposits and features in this zone were very intriguing and potentially conveyed important information about the early stages of the establishment of the broch.

The more time we spent in this trench the more that was borne out. We have long inferred that the preparation for building the broch involved cutting a large terrace into the hillside that it sits on. The logic for this hypothesis was that: in several places that we have reached the outer foot of the broch wall it is level to within a few centimetres, and this is despite the fact that it sits on a hill-slope or gradient of 1 in 20 (in other words the hill descends around 2 metres in height over the span of the 22 metre diameter broch). Obviously this would have made for an extremely sloping broch and interior without some modification.

At a distance varying between 3 and 6 metres out from the southern wall-face of the broch we could clearly see the natural glacially-derived clay only a few centimetres beneath the turf. Between there and the broch wall-face, however, it disappears and we have archaeological soils and features instead. This shows that the natural clay had indeed been cut into on its up-slope side. This year the southwest extension has allowed us to prove this terrace does exist and that the builders of the broch must have seriously landscaped the hillside by moving hundreds of tonnes of earth, clay and boulders to create a level platform for the broch. A huge effort was put into the formative stages of building the broch and shows us just what a substantial monumental project the building of the broch actually was.

Of Boundaries, Beads and other Bling!

Another surprise discovery from the SW trench extension this year was the presence of the ditch. Although we have known for some time (from geophysics and excavation on the northern side of the broch) that The Cairns, like many broch sites, was contained within a large ditched enclosure we hadn’t anticipated that the ditch trench would actually appear in the trench even if only present as an edge of the ditch.

We have been able to sample excavate the ditch and it turned out to be very rich in artefacts and animal bones, indeed, with lots of large chunks of pottery vessels and several metal objects; pins and the like. Ditches were clearly often receptacles for midden and refuse, however, they were also quite important symbolic boundaries between the community and the outside world, and this may be reflected in the types of materials, objects and deposition that occurs in them. So in future seasons we will do more work in the ditch. In many ways its a dramatic space, with lots to tell us in terms of the way the community lived and worked, but maybe also about their ideologies.

One of the artefactual highlights of the season also came from high up in the in-filling of the ditch. This was the so-called ‘proto hand-pin’, a type of decorative Iron Age bronze pin which are thought to have been in currency in the 3rd to 5th Centuries AD. As well as being a beautiful object in its own right, this little pin is instructive in giving us an early indication of when the ditch became fully in-filled.

And staying with flashy bling for a moment the other rival for artefact of the season has to be the little blue glass bead that came from one of the cells in the broch. This beautiful little object looks likely to be a 1st or 2nd Century AD Roman type, known as a bi-conical blue bead, and only a couple of others have been found at Scottish Iron Age sites, including Traprain Law in East Lothian, and Hownam Rings in the Scottish Borders. It may show how the site’s occupants were plugged into fairly extended exchange links with the Roman province.

Excavation of the Broch Floors

Inside the broch, the part of the team supervised by Rick Barton did a great job of dealing with the sensitive floor deposits. Work concentrated on the Western part of the broch interior. This area has previously been left at a higher level than in the east, simply as a result of our excavation schedule, and this season was our opportunity to explore this side of the broch more, and bring things into the same phase across the whole broch. It wasn’t long before interesting features were emerging. Under the uppermost rubble, a late hearth was uncovered occupying a central position within the western zone. It was large, and well-used judging by the heat cracking across the large base slab, but perhaps lacked the formality one would expect to see in primary, or original, hearths inside brochs. The vast quantity of charred organic material from deposits surrounding the hearth will yield lots of information about how this hearth was used. The way in which the hearth appeared to be sitting on top of a pronounced bump in the floor of the broch indicates it may be mounded up over an earlier hearth, and by the time we were finishing work this season there were hints of this situation in the form of edge-set stones and other heat-affected deposits emerging from beneath the edges of the hearth.

In the eastern side of the broch interior we undertook only a little work this year, as we want to wait until we have the west side down to the same level before proceeding too far, however, when we were joined by Dr. Jo Mackenzie, a specialist in soils and floors we undertook some excavation and sampling of the floors in this side of the broch. The floors were seen to be very rich and they possess very nice stratification (clearly laid down layers) that will help tell a very good story of life inside the broch two thousand and more years ago. The dark organic deposits seen in section show many thin layers of occupation, dark brown ones with charred plant materials, red peat ash ones, paler silty layers, etc, but when they are examined under the microscope it will be possible to see many more, otherwise invisible, layers that will be full of information on the different activities and activity areas within the broch; and the conditions prevailing at any point in the history of the broch.

The Broch Village

This year we were able to explore the extramural settlement, or village, that lies around the outside of the broch. We had a substantial window onto this settlement in the form of Trench Q, supervised by Dave Reay, and also the southwest extension also brought us into contact with the settlement. In Trench Q, a serious amount of rubble and ashy soils effectively sealed and masked the features of village buildings here, and it took sometime to reach the upper walls of buildings. However, Dave and his team were able to reveal the wall-tops of at least two, possibly three, Iron Age buildings across Trench Q. One of these has a nicely built curving wall and may turn out to be a roundhouse. The other was constructed by revetting into existing soils and rubble and may well be a building dating to later than the broch itself.

Meanwhile, in the southwest extension the same terrace cut discussed above, also contained the walling of a building that may well turn out to be part of the broch village. Indeed, this may reveal very telling information about the nature of the relationship between the broch and village. There is a debate in Scottish Iron Age studies about how contemporary the villages that surround brochs are with the construction of the brochs themselves. Some scholars favour the idea that villages developed around broch towers gradually, and were subsequent to the building of brochs, but others consider the villages to have been part of the plan from the outset, especially in Orkney and Caithness, perhaps, where the village buildings tend to have a very integrated, and planned appearance. The presence of a village building in the construction terrace of the broch may well tell us that the plans for the broch included village buildings from the outset. This will be a very significant piece of evidence in the debate, and it arises from the fairly unique way in which the broch builders chose to build and to deal with the topography, sculpting the hill slope in the first place.

The Souterrain

One of our aims this season was to deal with the deposits inside the souterrain on the eastern side of the broch. We excavated the deposits that in-fill the souterrain and took lots of soil samples to try to understand the composition of this in-fill. What’s more the way is clear for us to try to chemically analyse the floor of the souterrain to try to glean more information about how it was used.

A very odd feature of the souterrain seen in a previous season was the quern installation set up on the roof of the souterrain at its southern end. Essentially, two rotary querns had been set up inverted over an intentional aperture in the souterrain lintels. The central holes of the querns were aligned with the aperture, and the entire feature conveys the impression of being used to pour something into the underground passageway from above. There are several instances of Iron Age querns reused in this way to form a porous lid on pits in wheelhouses in the Western Isles, and in one instance it was suggested that there may have been libations being poured into them! Now that we have been able to excavate and acquire soil samples these will be subjected to phosphate analysis, amongst other analyses, to try to discern what trace there might be of any substance that was being poured into the hole in the roof.

Different ways of seeing the site: aerial images and 3D modelling

This year at site we have been able to take advantage of the burgeoning new technologies like never before. The use of UAV’s (commonly known as drones) has been rapidly revolutionising the elevated perspective that archaeologists are able to get on archaeological sites. We were massively assisted in gaining this broader context this year by the UAV work of artist Rik Hammond and my colleague Dr. James Moore. Their use of the UAV several times during the course of the site has given us a fantastic aerial perspective on the site and its landscape.

The second new technology requiring acknowledgement here is that of 3d computer modelling. Throughout the period of the excavation one of our MSc students Jim Bright has been developing his skills in this domain. The results of some of his models have been posted here already, and there will be many more models. These are not just aesthetically pleasing models of the features and artefacts but actually useful in research terms as they allow us to gain privileged perspectives otherwise difficult or even impossible to acquire.

Meanwhile, another colleague Dr. Hugo Anderson-Whymark has produced a complete, whole site 3D model of The Cairns. This is a massively useful and impressive piece of work, that again allows us to interrogate lots of different aspects of the features and structures of the site. Again it provides an incredible tool for visualising the site in all its detail. The link to Hugo’s fabulous model is given here: https://sketchfab.com/models/db98e708e7e14e70aac55d8ee027c85b Here’s Hugo’s model and a little blog within the blog that he has prepared for it: Enjoy!

The Cairns Broch Excavation, Orkney by Dr Hugo Anderson … sketchfab.com The Cairns Broch Excavation, South Ronaldsay, Orkney The Cairns is an Iron Age broch – a massive circular structure with thick defensive walls that would have risen …

‘Over the last few years I’ve produced 3d models of various archaeological sites and artefacts in Orkney further afield and on Monday I finally got the chance to scan The Cairns. It’s a large and complex excavation site, with lots of thin projecting stones that present a real challenge for 3d modelling – the sort of challenge I like! The 3d modelling technique I use is ‘structure from motion’ photogrammetry which produces 3d models from overlapping photographs taken on any digital camera. In total I took 1648 photographs for the site over a few hours, when the sun and showers permitted. Most of these images were taken vertically from a pole, but within the broch I took images from a range of angles to capture the complex arrangements of stone orthostats. After 10 hours processing with Agisoft Photoscan on my PC, the model I’ve uploaded to Sketchfab appeared on my screen. This model offers a great way to explore the site, as the archaeology is more easily understood from above, but it also forms an important part of the site archive as the model is tied into the site grid and captures the vast progress made in the 2017 excavation season’.

And finally…

All in all, it has been a very fruitful and enjoyable season, with a lot learned about the nature of the site, from its beginnings to the end, major features of the site such as the excavation of later broch floors, the broch construction platform and the ditch will immeasurably help us to understand the character of the settlement, and the finds this year have been very rich and highly useful in a number of ways to elucidate issues relating to dating, the status of the community and their depositional practices.

Now some thank you’s! I’ll take this opportunity to thank the entire project team for their unstinting humour, patience and enthusiasm. Without them the site would of course remain unexcavated, and its only through their sterling efforts that we begin to understand what was going on at the site more than 2000 years ago!

This year the donations made by the visiting public have been more substantial than ever before. We benefitted from the largest number of visitors to the site of any season so far, and they were very generous in their expression of support for the project. The funds will now be spent on important aspects of furthering the research, such as radiocarbon dating the beginning of the broch, and understanding the major metalworking episode on the site. I would like to thank all of the visitors and donors, and for allowing us to communicate our findings at the site.

Finally, I would like to thank Charlie and Yvonne Nicholson and all of their family and friends in South Ronaldsay for their many acts of assistance and generosity. Our time at The Cairns is made possible, enjoyable and very amiable due to their great kindness.

Thank you!

Martin Carruthers, Site Director.

Whilst the excavation at The Cairns has been up and running, myself and Gordon Higgs (a student from Sheffield University) have both been undertaking professional Placements with the project to undertake geophysical survey in the fields surrounding The Cairns.

The aims of this survey were to investigate the landscape of the Broch and to identify the precise location of the enclosure ditch around the front, (Eastern side) of the broch and to identify any evidence for additional human activity nearby.

Two different types of geophysical survey were used, resistivity and magnetometry. Resistivity survey uses an electric current to measure the resistance of the soil, from which it is possible to identify disturbance (including past human disturbance) in the soil. Resistivity is ideal for detecting ditches and stone built features, because these features will have a different resistance from the surrounding undisturbed soil. Magnetometry survey measures changes in the magnetic field which can detect heat affected and burnt features such as hearths or fuel ash middens, metal artefacts and other past disturbances.The results of the survey show that the landscape has been heavily ploughed in the recent past and has disturbed archaeology in places. Nevertheless, the ditch surrounding The Cairns has shown up in both types of survey. Indeed, the anomaly on the survey results showed that it appears to be a double ditch feature. These substantial ditches are passed through by a linear feature, which is a couple of metres wide and runs from the broch sown slope towards the coast. This feature appears to be an ancient ‘hollow way’, or sunken track, and could also be partly related to a lintelled passageway referred to by the antiquary the Rev. Alexander Goodfelow over a hundred years ago.

At the bottom of the field just south of The Cairns an earlier geophysical survey showed an arc in the corner of the survey. A test pit was excavated there earlier this year and identified a curving stone feature that looks like a well-built wall within an ashy soil matrix, and a fragment of a saddle quern of prehistoric type. When we extended the geophysical survey to cover more of this anomaly it showed a series of semi circular features with possible central hearths. These anomalies could be related to houses in a fairly large settlement and/or associated structures like workshops.

There may be as many as 6 or 7 of these buildings. These look very similar to Bronze Age houses seen in the World Heritage Area of Stenness/Brodgar and in other locations in Orkney and Shetland.  This exciting prospect could be tested by excavation to confirm the nature of these features.

We were hoping to find the continuation of these structures in the next field to the south, however, the remains have either been ploughed away or are smaller than expected and obscured by the field boundary itself. This lower field did show another possible circular feature and a very strange linear anomaly on the resistivity results. An igneous dyke (or possibly two) run through the lower field which was easily identifiable by our magnetometer results.  This natural geological feature is interesting in its own right as we know prehistoric communities treated volcanic dyke rock as a resource, sometimes quarrying such sources of igneous material for stone artefacts and crushed up the rock for the ‘temper’ that they mixed into the clay of ceramic pots.

There are many more discoveries in the geophysics survey undertaken and the survey work has confirmed that The Cairns broch was not an isolated feature in an empty landscape, it was part of an active, evolving landscape and it would be interesting to test some of these features to confirm if some of them are contemporary with the broch. Even though the weather seemed to be against us some days, the results from the geophysical survey have been very informative, hinting at the wider landscape and future stories for archaeologists to uncover.

Leonie Teufel, MSc. Archaeological Practice Student, UHI

Today was the second last day on site. Despite the start of the process of covering up the site in earnest, we nevertheless still carried out some exciting work.

In the broch, yesterday’s blogger; Jo, continued to take special micromorphology samples from the floors. Working in the ‘central passageway’, which is a kind of corridor space that permitted the occupants to access several rooms set against the southern side of the broch, Jo was able to take a sample and reveal a lovely floor deposit underlying the dark, organic occupation deposits. This is really good news because it means that almost all of the areas that we have investigated floors across the whole of the eastern and central areas of the broch we have this fairly standard process of floor-making in evidence. What happens is that nice clean clay floors are laid down, presumably as a kind of beaten earth floor and then these floors are lived and worked upon. This human activity then produces detritus and organics that come to look like thick black charcoal rich deposits. These contain wonderfully rich sources of info’ about how people used the broch.

Today when Jo was working in the floors she also found a piece of unburnt wood in one of the dark lenses of occupation. This is a very unusual find as, obviously, wood that hasn’t been charcoaled is prone to decay!

Elsewhere in the broch, in the western zone, work on the occupation deposits around the late hearth, produced lots of antler, including what appeared to be an antler tool, perhaps for tending the hearth, as well as lots of other animal bones, and what appears to be the edges of an earlier, probably more formal hearth underlying beginning to emerge.

We will be concentrating on the final cover up of the site tomorrow, so only a few things require to be completed and recorded now- but it has been a very good season, and I’ll be rounding that up in tomorrow’s blog. Tomorrow we’ll also tell you about all the fascinating geophysical survey that has been happening at the site while we’ve been digging.

But as a treat here’s an extra blog piece from Rik Hammond below. Rik’s an artist that has been working alongside us on site for several years.

Martin Carruthers, Site Director.

My name is Rik Hammond and I’m a visual artist based in St Margaret’s Hope – just up the road from The Cairns, here in South Ronaldsay.