Reconstructing Oakbank Crannog

By Barrie Andrian
Excavations in Loch Tay, Scotland, revealed the remains of a crafted Iron Age dwelling. How were these remains interpreted to create the lifelike reconstruction in existence today?
Scottish Crannog Centre, Loch Tay, Scotland 

Pioneering excavations

Crannogs, or artificial islands, are found throughout the lochs of Scotland and Ireland. In Scotland they were ‘rediscovered’ in the 19th century as a result of landowners draining small lochs to gain more agricultural land.

Following a detailed survey in Loch Tay in 1979, the early Iron Age site of Oakbank Crannog [/history/trail/archaeology/iron_age/recon_oakbank_cran_fact_file.shtml] , off the village of Fearnan, was selected for pioneering underwater investigation. During several short seasons, this first ever underwater excavation of a crannog revealed well preserved 2,500-year-old structural timbers, domestic utensils, food remains and textile fragments.

The discovery of so many clues about our Iron Age ancestors was exciting, but how best to interpret them? This is the story of how evidence found at the bottom of a loch led to the reconstruction of a crannog four miles from the original site.

Houses on water

Image of roof being built with hazel rods
Building the roof with hazel rods
As the excavation progressed, all of the evidence from Oakbank Crannog began to paint a very detailed picture of some aspects of the lifestyle of our Tayside Early Iron Age ancestors.

Finds of grain, a plough, animal droppings and a butter residue in a wooden vessel pointed to a farming lifestyle. The archaeologists were puzzled, though, as to why farmers should wish to live on the water. They also wondered about the building methods the ancients could have employed. How had they managed to build a roundhouse on stilts out in the water?

The team decided to try to rediscover ancient technology first, and then to recreate a life-sized crannog based on excavation results at Oakbank Crannog and on related research.

'They had to learn forestry and woodworking skills on the job ...'

The project was set up under the auspices of the Scottish Trust for Underwater Archaeology [/history/trail/archaeology/iron_age/recon_oakbank_cran_fact_file.shtml] , involving Trust members, and students and staff from Edinburgh University. In 1993 the team carried out tree felling and pointing with a replica axe, and carried out pile-driving experiments, before starting work on the crannog in 1994.

They had to learn forestry and woodworking skills on the job, and harvested nearly all the materials required from the Loch Tay area. Re-discovering ancient pile-driving skills was not an easy task. The trees were heavy and difficult to raise upright from the water surface. Once the trees were upright, however, the team discovered a simple, if tiring, method to achieve the driving.

They lashed a short pole across the tree and used it to swivel the pile from side to side. The momentum was sufficient to drive the pile into the lochbed. While there is no guarantee that this is the method the ancient crannog builders used, it is simple and effective, and certainly one that they could have practised.


Image of timber supports for the crannog
Close-up of tool marks on an underwater stake
The foundation structure at Oakbank Crannog has not yet been completely excavated, so the supporting framework for the floor of the reconstruction was based partly on evidence and partly on common sense and simple building techniques.

The floor timbers were added next, placed in the same way as discovered in the excavation. Then supports were put in place for the roof and the roof poles added to create the skeleton of the house. The height of these was chosen by informed guesswork based on the dimensions of the house.

'The modern builders chose to use reeds from the River Tay ...'

Flexible hazel rods were used to link the roof poles together to provide a secure frame for the thatch. No intact roofing or thatch has been discovered or recognised yet at Oakbank, but the volume of bracken in the site suggests that either it, or straw from the cereal crops, could have been used for thatching.

The modern builders chose to use reeds from the River Tay instead, as they are the most durable of natural thatching materials, and they were local and readily available in bulk.

The team made the walls for the reconstruction as wattle hurdles, based on the fallen example excavated at Oakbank. No walls as such have been discovered, so no one knows whether the ancient builders plastered, or daubed, the walls to prevent draughts. In the absence of evidence, it was decided not to do this, as there are other less permanent methods to use to stop draughts, such as hanging skins over the hurdles.

Similarly, there is no evidence for the decking around the outside of the house, so this also is based on a combination of informed guesswork and parallels from other crannog excavations, such as Milton Loch in Dumfrieshire.

Experimental technology

Image of divers and platform at Loch Tay, Scotland
Divers search the loch for clues about the existence of a crannog
While the crannog was created as authentically as possible, the reconstruction cannot be totally accurate as there is no complete example from which to work, and the excavation at Oakbank was not finished as the reconstruction progressed.

There may be other, better preserved structural information in lower deposits, and excavations of other contemporary crannogs in the future may provide details to fill the gaps in our knowledge. Archaeology makes an invaluable contribution in this respect - no one can answer many of the questions raised at Oakbank with certainty until there is evidence.

'These houses were clearly designed to withstand gale force wind and waves ...'

A great deal has been learned by constructing this building, and this continues to be the case as the crannog is monitored and maintained. The logic of a free-standing structure in a high-energy loch becomes apparent whenever there is a storm. These houses were clearly designed to withstand gale force wind and waves, and so far the reconstruction has withstood wind speeds in excess of 100mph.

It is, however, a living structure, which requires a rolling programme of repairs to maintain it in good order. This problem is probably exacerbated by the building being open to the public, but untreated trees do not last forever, and the excavation evidence points to similar problems experienced by our Iron Age ancestors.

Interpreting the evidence

Image of piles used to reconstruct the crannog
An original pile from Oakbank Crannog
Several phases of construction and repair have been identified at Oakbank Crannog, although the relationship between the main mound and what appears to be an annexe has yet to be determined.

The experimental reconstruction was possible due to the thousands of timbers recorded at Oakbank Crannog representing uprights, floors, and woven hazel hurdles. The juxtaposition and volume of these timbers demonstrate that this early Iron Age crannog was built initially as a free-standing dwelling supported by stilts or piles.

'... fibrous plants were used to make ropes for lashing timbers ...'

Analysis of the hazel hurdles indicates that the crannog farmers were also woodland managers. They coppiced hazel and other native species to provide a regular supply of timber for structural needs, fuel and domestic utensils. The well preserved tool marks on a range of timbers were the subject of a separate research project, and suggest the use of iron rather than bronze axes, knives and other tools.

There was also evidence that fibrous plants were used to make ropes for lashing timbers, tethering animals and carrying goods. Analysis of the abundance of bracken in the site showed it was harvested all year round. It would have been used to make the floor more comfortable and warm, to make the walls draught-proof, to provide animal and human bedding, and probably to help thatch the roof.

Finds of charcoal, ash and sizeable stones near the middle of the house may represent part of the central hearth, where the fire would have been in almost constant use for cooking and heating the building.

Iron Age artefact

Image of an Iron Age plough found at the Oakbank site
Iron Age plough found at Oakbank site
The range and preservation of artefacts and other materials at Oakbank Crannog helps us to understand the loch-dwellers’ lifestyle, in the same way that the structural remains indicate how they may have built their homes.

Deposits of dung and droppings tell us that the Oakbank farmers kept cattle, sheep and goats, while the grain, a quern stone, and the discovery of an ard (or plough), point to cultivation. The shore and hills opposite Oakbank proved to be good arable land.

Further analysis has revealed that the crannog farmers were fairly well off, growing not only a staple crop of barley, but also two different kinds of wheat. Rare in the record of Iron Age Scotland, the wheat finds also are an indicator of status.

'... the plentiful evidence about the diet of these crannog farmers is exciting.'

The crannog farmers grew emmer wheat and spelt wheat, but the latter was not thought to have been introduced to Scotland before the Romans. The discovery in Loch Tay pushed this theory back at least 500 years. Triticum Spelta is still cultivated today providing a sense of continuity with the past.

In our modern age of heightened food consciousness, the plentiful evidence about the diet of these crannog farmers is exciting. Finds of jawbones and long bone remains indicate not only that the animals were valued for their fleece, but also they were butchered when necessary.

The butter residue in the wooden vessel indicates the crannog farmers also knew how to exploit their animals for dairy products, and we can surmise that they made cheese as well as butter. The farmers may also have fished, though no fish bones have been discovered so far. Several perforated stones have been discovered, however, and these may have served as net or fishing weights.

Ecological clues

Image of textile fragment found at the site of Oakbank Crannog
Textile fragment found at Oakbank site
Pollen analysis and plant remains point to a varied and nutritious range of food. Apart from the meat and grain produced from their farms, the crannog people harvested the wild and cultivated herbs, greens, and the roots of plants before anyone knew what vegetables were.

Many people assume that food in prehistory would have been a matter of survival rather than taste. However, evidence of cabbages, wild carrots, wild turnip, nettles, ramsons or wild garlic, meadowsweet, fungi, millions of hazelnuts, wild cherry and sloe stones - and more - suggest plenty of scope for creative cooking. Add to this the earliest discovery of cloudberry from a settlement site in Scotland, and we are presented with the capacity for a very palatable Iron Age feast.

'The cloth fragment was made from drop-spun sheep’s wool woven in a 2:1 twill.'

The piece of cloth from Oakbank Crannog is of particular interest, as such finds are uncommon from early Iron Age sites in Scotland. The cloth fragment was made from drop-spun sheep’s wool woven in a 2:1 twill. This is a robust, hardwearing type of cloth, which suggests the crannog farmers had sophisticated weaving skills. There was no trace of dye remaining in the cloth but, after 2,500 years of immersion in water, this was not surprising.

The future of our past

Image of Iron Age pottery fragment
Pottery fragment found at Oakbank site
Underwater excavations have taught us a great deal about the diet and sophisticated lifestyle of these crannog farmers, but there are still many questions left unanswered. In the absence of human remains and icons, we can make no definitive statements as to burial practices or spiritual beliefs.

Furthermore, while comprehending the logic of such a structure, we can still only surmise the reasons for building in the water in the first place. Certainly, there are many practical advantages including protection, sanitation, and the creation of a midge-free zone. However, given the effort and resources required, it is likely that these homes were built to make a statement on behalf of wealthy or powerful owners.

'... it could take generations to fully understand these structures ...'

Necessarily, this picture is but one in a gallery of many blank screens. Despite the hundreds, if not thousands of crannogs, to be investigated, there is no integrated research strategy and no regular core funding to further their study. Given the backdrop of these challenges and the current level of activity, it could take generations to fully understand these structures, the people who created and lived in them, and their context within the rest of Iron Age Scotland.

Published on BBC History: 2005-01-25
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