2018 Knowe of Swandro Excavation

The 2018 season saw the completion of the excavation of the Pictish Smithy (Structure 3) and the start of a new phase of the project with the excavation of the suspected Chambered Cairn forming the Knowe of Swandro. 

The Pictish smithy's floor had been identified in 2017 and revealed significant metalworking debris suggesting both iron and copper working, with spheroidal slag and hammer scale suggestive of sophisticated blacksmithing including fire welding. The presence of a number of crucible fragments strongly pointed to the structure having been used for copper ally working. Subsequent analysis of the crucible fragments by Dr Gerry McDonnell using X-Ray Fluorescence (XRF) indicated that the crucible fragments were used to cast an alloy with a high zinc composition forming a brass rather than a bronze (with a higher tin content in the alloy).  In the summer of 2018 Dr McDonnell supervised the excavation and sampling of the floor of the Pictish building. The floor was carbon rich and the hearth demonstrated two phases of use. In between the upper hearth fragment and the lower primary hearth a further fragment of crucible was found. The excavation revealed further evidence of metalworking, with crucible fragments and the remains of several fragments of fired clay from a tuyère, which would have protected the snout of the bellows. Magnetic susceptibility and XRF survey of the floor, together with the in situ remains of the furnishings of the building, have provided a unique understanding of the use of space within the structure. 

Dr Gerry McDonnell using XRF to locate areas of copper working on the floor of Structure 3

The building was clearly semi-subterranean in nature, with a shallow set of steps leading into a passage flanked on the left-hand side by the wall of the structure and by a large orthostatic slab on the opposing side. A door would have opened into Structure 3, the doorway being defined by an in situ threshold stone and door pivot. Anyone entering the building would have to enter to the left (clockwise) of the hearth and its back-slab that would have protected the hearth from drafts. The strongest signatures of copper working determined by Dr McDonnell's detailed XRF analysis of the floor surface indicated the working position of the smith would have been on the left-hand side of hearth, facing the doorway and hearth back-slab and in front of two beach cobbles set into the floor. These cobbles, one an elongated block and the other smaller and squarer in shape, had clear percussion damage indicating their use as anvils.

 

Whilst preparing to illustrate the larger cobble, archaeological illustrator Alan Braby noted carbon staining appearing to represent the finger or hand marks of the smith. Dr McDonnell's survey of the floor and the presence of the tuyère fragments suggest the bellows were located on the opposite (right hand) side of the hearth. A cupboard or aumbry constructed within the wall of building would have been to the left of the smith and may have been used either as storage or the location of a lamp. The layout and sophisticated design of the building strongly suggests that this was a purpose-built smithy.  The hearth furnishings seem to have been constructed as part of the building’s primary usage. The semi-subterranean nature of the building and the location of the doorway formed an effective means of reducing natural light.  Added to this, the doorway presented clear evidence of two means of barring the door, one from the inside, further reducing any light incursion.  The observation of flame colour by the smith would have been critical to enable them to gauge metal temperature. It is worth noting that a second bar hole was present, indicating that the door could also be secured from the outside.

Beach cobble used as anvil in the Pictish Smithy; hammer marks can be seen on the upper surface and what appear to be carbon handprints on the side and edge

This metalworking building (Structure 3 the Pictish Smithy) had been constructed within two parallel single faced stone walls that had in previous years suggested the presence of an earlier building. Further investigation in 2018 suggested that this earlier stonework actually represented the stone revetments of a ditch. The fill of this suspected ditch below the ash and carbon-rich floors of the Pictish smithy had been compromised by the tidal action of the sea, consisting of vacuous rubble with lenses of beach sand. A small fragment of plastic was observed within this material, although the layers of floor above this fill were intact and undamaged. The pressure of the sea from tidal and storm surges appears to have horizontally penetrated the archaeology below Structure 3, removing finer archaeological sediments. This erosive action has affected the walling of Structure 3 (the Pictish smithy) on the seaward side and seems to be responsible for the subsidence of the wall into the top of the infilled ditch.

Sondage below the Pictish Smithy showing (at left) the possible stone revetment wall of a ditch, with Alan Braby at work drawing the section through the building

This year, excavation commenced on a new area encompassing the central zone of the Neolithic chambered cairn. The cairn was revealed in previous investigations in 2012 and 2015 as a series of casement walls and packed core under the boulder beach around the high tide line. The new area included the entrance first identified in 2016 and further defined in 2017; it also took in a new area on the landward side of the entrance. Excavation revealed a complex archaeological sequence in contrast to the eroded sequence investigated under the boulder beach in 2012 and 2015. Excavation in 2018 within this landward zone indicated a structural sequence that was secondary to the monumental structure interpreted as being the Neolithic Passage Grave.  

 

This structural sequence comprised of a round house form (Structure 6) which had been inserted into the monumental structure, re-using and extending the original entrance passage. The structure was represented by an inner-faced wall with a difference in alignment to the earlier casement walling. This round house appears to have had a complicated history of collapse, rebuilding and use, being subdivided by later structural elements characteristic of the late Iron Age or Pictish period. This late phase was represented by a dividing wall and orthostatic alignment forming a large inner cell on the landward side of the passage (Structure 5) with a doorway that had later been blocked by stone walling.

 

The preservation in this area suggested a complex sequence of modification, with a deep stratigraphic sequence surviving. An infill of mixed midden material, rich in animal bone and pottery, was recorded inside this cell whilst outside the wall and blocked doorway there was evidence of more than one structural collapse of the round house, the latest involving the fall of very large orthostats, one of which lay against the blocked doorway. Several of these elements suggested the collapse of corbelled roofing structures. This new exposure of the inner end of the passage provided evidence of structural collapse. Two long and substantial stone slabs just under 2m in length were found lying along the axis of the passage and partly inside the roundhouse. These stones might represent either a pair of fallen orthostats or uprights, or possibly lintels associated with the roofing of the passage. If these stones were set upright they would coincide with a change in width and orientation of the passage at the point where the secondary Iron Age roundhouse was inserted.

Looking down the passageway of the chambered tomb showing some of the rubble and possible collapsed roofing slabs. Standing figures on the right are in the later Iron Age house inserted into the top of the tomb.

The removal of the boulder beach overburden of the area of cairn previously assessed was deeper than expected and indicated that the archaeology here had been badly truncated by the sea. The area at the top of the boulder beach which had been exposed in 2015 had suffered greatly in the intervening years despite the archaeology being covered; much of the finer sediments had been washed out, the survival of archaeological sediment-based deposits was poor and in contrast to the material on the landward side. The suction of the finer deposits caused by the receding tide seems to be the main cause of this. This effect seems consistent with the evidence for Structure 3 discussed above. Very little of the tertiary Pictish deposits survived the aggressive action of the sea in this zone. 

The scoured out cist below the chambered tomb which may possibly be a later Bronze Age burial inserted into the tomb mound

Within this eroded zone of the Cairn a stone cist was identified. The fill of the cist had been completely scoured out by wave action and entirely replaced by beach deposit. However, a fragment of steatite vessel was found on the surface of the archaeological deposits just below the cist. This fragment appears to be Bronze Age rather than Norse in character and suggests the possibility of a Bronze Age use of the cairn. Adjacent to this cist the top of a corbelled cell was identified, possibly representing part of a side chamber to the cairn. This feature was recorded and carefully packed and will be fully investigated next year.

The entrance to the corbelled cell which may be part of the body of the chambered tomb (the black-and-white scale is 50cm long)

Outside the wall of the cairn, a corridor-like structure had been identified in 2017. This structure was built against the outer wall face with several in situ lintels set upon two scarcement-like ledges. The extended excavation area allowed more of this structure to be investigated. The excavation revealed further parts of this corridor, which appears to have at least two major phases of construction with its secondary and latest use dating to the Pictish period. A poorly-constructed single faced wall formed the end of this secondary passage.  This single-faced wall stratigraphically sealed an earlier and better-constructed corbelled wall associated with the ledges and lintels. The backing material to both of these end walls was composed of midden, including a layer rich in limpets and pottery. Two sequences of backing material corresponding to the two phases were identified. The lower fill sealed the top of the corbelled end to the lintelled corridor.  A series of slabs at a 60-70 degree angle appeared to represent structural elements consistent with the collapse of a corbelled roof; they sealed the material backing the secondary and poorly-constructed single faced wall.

Corridor outside the chambered tomb at Swandro with a roughly built blocking wall, excavated by the Time Team's Jackie McKinley.

The opposing long wall of the secondary use of this corridor was formed by several large orthostats. These orthostats were backed by a mixed midden-like infill, which was contained by a much earlier well-constructed wall of a distinctly different build. This earlier wall had been truncated by the construction of Structure 4, a Pictish building partly excavated in 2015 during the evaluation of the eroded beach section. 

Excavation of Structures 5 and 6 and the primary cairn will continue in 2019.

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Swandro - Orkney Coastal Archaeology Trust Scottish Charitable Incorporated Organisation No: SC047002 

Patron: His Royal Highness The Prince Charles, the Duke of Rothesay

Registered office: Bayview Birsay Orkney KW17 2LR   email: info@swandro.co.uk