MHG62838 - Iron age occupation site - Swartigill Burn, Thrumster


An Iron age occupation site on the south side of the Swartigill Burn near Thrumster. Investigations are ongoing and full interpretation of the site awaits final analysis.

Type and Period (1)

  • OCCUPATION SITE (Iron Age - 550 BC to 560 AD)

Protected Status

  • None recorded

Full Description

An Iron age occupation site on the south side of the Swartigill Burn near Thrumster. Investigations are ongoing as of 2023 and full interpretation of the site awaits final analysis.

Members of the Yarrows Heritage Trust photographed and recorded the eroding elements of the Burn of Swartigill Site for the first time in 2004 during a survey of the two known medieval-post-medieval settlement sites to the northwest (see MHG48275) and southwest (see MHG). Walling was noted at both the eastern and western extremities of the eroding section which extended for circa 10m along the southern bank of the Swartigill burn. At the time it was assumed to be a similar site to, or at least associated with, the two already known. <1>

The eroding site was recorded during a major landcape survey around the Loch of Yarrows by RCAHMS (Visited by JRS, IF 27 July 2004) and Caithness Archaeological Trust in 2004. What may also be the remains of a structure are visible eroding out of the S side of the burn, some 33m SE of the first farmstead. What appears to be two sections of drystone walling, measuring up to 0.6m in height and 11m apart, seem to retain between them a mass of small boulders, slabs and stones. The upper part of this stony mass is relatively loose and set within topsoil, but the lower part is set within a matrix of clay containing fragments of charcoal and burnt bone. Within the mass there is a structure resembling a small cist or culvert built of thin slabs and measuring about 0.3m square in section. Its interior extends at least 0.4m back into the face of the eroding bank. <2> <3>

A Ground Penetrating Radar (GPR) survey was carried out by CFA Archaeology in 2007 at Swartigill as one of five sites in the vicinity of Loch of Yarrows selected in order to assess the applicability of GPR survey on a range of different sub-surface peat formations. The site of Swartigill Burn was chosen as part of the study owing to the presence of known archaeological remains within a flat area of alluvium alongside the burn of the same name. The extent of the structural remains were not known and it was hoped that the result of the GPR survey would shed light on the extent of the remains, as well as test the effectiveness of the GPR equipment over a different soil regime. The results were mixed. While it appeared that the technique successfully defined the potential limits of the postulated site, it failed to clearly delimit individual features such as walls. Although this was likely to be a reflection of both the nature of the technique and the nature of the archaeological deposit as GPR cannot differentiate between in-situ stonework and rubble. <4>

A small community based archaeological evaluation was carried out by Yarrows Heritage Trust at the site in 2012 with the objective of prospecting for the remains of the township of Swartigill. Two settlement sites had been known for some years, one to the north of the burn and one to the south. The third site, comprising walling and rubble eroding out of the bank of the burn, had been recorded by photography in 2004. This site was being and continues to be undercut by the burn and suffering erosion by sheltering sheep. Large stones in the burn-bed suggested that much has already been lost. The objective of the evaluation was to clean-back and record the full eroding section. It was initially thought that the remains represented a dam and / or mill. A box section feature may have been Iron Age but it was high in the section and could be a 19th century French drain. The results were totally unexpected. Pottery recovered from the erosion surface comprised fabrics consistent with the early Iron Age. Finer quality pottery was also found that was consistent with a late Iron Age date; possibly Pictish. Current knowledge holds that these pottery types have been exclusively associated with broch sites. <1>

A fluxgate gradiometer survey, an earth resistance survey and a ground penetrating radar survey were carried out by ORCA at the site in 2014. The survey was aimed at characterising the extent and the nature of the site being eroded by the burn. The gradiometer survey highlighted an area measuring 25m x 30m, presenting strong magnetic variation likely to be associated with anthropogenic activity and potentially the presence of a settlement. The earth resistance suggested, within this area of enhancement, the presence of a potential sub-rectangular structure measuring 10m x16m. The ground penetrating radar helped clarify the nature of some anomalies visible in the gradiometer and earth resistance survey. Previous work on the site, including the cleaning back and recording of structural remain in the Burn of Swartigill section produced a substantial quantity of early and late Iron Age ceramics, and it is possible that the results of this geophysical survey may have unveiled a late Iron Age settlement, with a ‘wag’ or a ‘figure-eight’ building, present. It was hoped that the data gathered during the survey would enhance the previous work undertaken by members of the Yarrows Heritage Trust and would assist in the planning of further work at the site. <5>

A fairly small-scale trial excavation was undertaken by ORCA and Yarrows Heritage Trust at the site in 2015. The work was undertaken with good attendance of volunteers from the local community. The aims were modest and linked to scoping out the site for a potential, more expansive, future piece of work. One of the project objectives reflected the desire to ‘ground-truth’ the geophysical survey undertaken by ORCA in 2014. This survey had potentially pointed to the presence of a substantial rectangular building form, perhaps a post-broch Iron Age period ‘Wag’ a form of building well-known in Caithness and Sutherland. A second aim was to try to establish something of the character of archaeological remains that had been discovered eroding out from the side of the Burn and recorded and reported on by Yarrows Heritage Trust in 2012. A small excavation trench (c.3.5m x 3.0m) was placed to incorporate part of the erosion front, a more extensive area behind and a long narrow extension c.3m running southwards. While a series of small trial trenches (1x1m, 1x1m and 2x1m respectively) were opened to give key-hole views into some of the other geophysical anomalies picked up in the original survey.

Substantial alluvial deposits from the floodplain of the burn were found to shroud archaeological remains to the south of the burn frontage itself, but there was a substantial mass of stone work, rubble and well preserved archaeological features lying beneath this alluvium. This was traceable as a fairly unprepossessing low rise in the modern ground surface. It can be tentatively suggested that the orientation of linear wall lines revealed in the main trench indicate a match to the rectilinear anomaly apparent in the geophysics, and these may reflect a long building orientated with its long axis at right angles to the stream. A pronounced gully or channel was identified running through the mass of rubble in one area. A section through the gully located a large subterranean stone-lined feature, probably a drain. The drain implies some element of water management, possibly beyond that required in a normal domestic space, and it could be connected to a range of possible different activities. Samples taken from the drain will hopefully yield well preserved environmental evidence and may even have implications for the role of the site and its proximity to the Burn of Swartigill.

Near to the burn it was possible to link the previously evaluated archaeological remains present in the erosion front with those in the main trench and in several of the small test trenches, and to establish that certain previously recorded massive blocks of stone and other features were indeed parts of wall lines and wall faces seen more clearly in the main trench. A significant assemblage of diagnostic ceramic sherds including well made, decorated Iron Age pottery, was recovered from contexts both abutting, and overlying, the wall lines, and much of this ceramic material is identical to sherds recovered in the earlier stage of work. A quern rubber came from the rubble mass and a hammer stone from the fill of the drain feature. Slightly more surprising, given the relatively modest scope and scale of the excavations but no less welcome, was the discovery of a copper alloy artefact. In appearance this was a small abraded triangular fragment abraded smooth but nevertheless preserving indications of a deeply set ‘cell’ perhaps for an enamel inlay. This would appear to have been a relatively valuable item from something like a brooch or a decorative fitting.

A small programme of radiocarbon dating was included in the project with the intention of providing very preliminary dates for the site. Two radiocarbon dates were obtained from trench 1. Deposit 011, is the dark grey silty deposit that abutted wall 010 close to the burn, and which contained high quantities of pottery during the 2015 season and in the previous exploratory work undertaken by Yarrows Heritage Trust. This deposit returned a date (lab code: Poz-87142) of 366 to 192BC, at 95% confidence, or 357-204BC at 68.2% confidence levels. The second sample submitted for dating was from deposit 009, the slightly sandy silt that had sealed a fairly extensive portion of the upper elements of trench 1 and, if the stratigraphy has been read correctly, should date to later than the pottery-rich deposit. The date (lab code: Poz-87141), returned was 198-47BC at 95% likelihood, or 170-61BC at 68.2% certainty. In submitting these specific deposits for dating, it was intended that this would provide some reassurance of the in situ nature of the depositional sequence and demonstrate that the in situ pottery deposit had not been disturbed by later activity.

The dates from Swartigill are also highly significant when considered in comparison to dates obtained from the excavations at the nearby Yarrows broch (also known as Thrumster Mains Broch - see MHG2043), where it was suggested that the broch was established in the Third Century BC (2012, 35). This may suggest that the broch at Yarrows was founded a little later than the earliest dates obtained for Swartigill. Since the dates from Swartigill cannot be considered to relate to the earliest activity at the site, it is tentatively suggested here that Swartigill represents an early Iron Age site, occupied before and during the establishment of brochs in the wider landscape. Swartigill may therefore represent an opportunity to explore the social and historical conditions that prevailed at an important moment of material change during the Iron Age period of Caithness and of Atlantic Scotland more broadly. <6>

Further excavation was undertaken by the Archaeology Institute (ORCA), UHI and the Yarrows Heritage Trust in 2017. The structural remains recorded during the excavation aligned with areas of high resistance identified in the previous geophysical survey and formed a large sub-circular structure with an internal area measuring c6m east-west by 5m north-south. A small number of artefacts were recovered, including a small number of prehistoric ceramic pottery sherds and a whetstone reminiscent of 10th- and 11th-century artefacts from Norway and Iceland, though further analysis of this find would be required before its provenance could be confirmed. The presence of this artefact raised the possibility of Viking period or early medieval activity on the site which post-dates the demolition of the structure. Deposits on the west side of the structure contained abundant inclusions of charcoal, charred grain and fragments of magnetic material. The latter may represent hammer-scale, indicating evidence for metalworking, though further analysis would be required. The dating evidence for the site so far indicated that there was potentially an early Iron Age phase of occupation at this site. There was, however, a strong possibility that the primary phase of occupation may pre-date this activity, since the deposits which have so far been investigated appeared to be associated with structures which may themselves be secondary to an earlier phase of building. Swartigill Burn could potentially represent an opportunity to investigate a site from the transitional time period between the late Bronze Age and early Iron Age, an important and relatively under studied aspect of northern Scottish prehistory. Further C14 radiocarbon dating will be undertaken from deposits sampled during this most recent excavation season in order to further investigate the antiquity of the site. It was recommended that further seasons of excavation be undertaken at the Burn of Swartigill in order to define its extent, date, function and preservation. <7>

Sources/Archives (7)



Grid reference Centred ND 3211 4573 (30m by 30m) (2 map features)
Map sheet ND34NW
Civil Parish WICK
Geographical Area CAITHNESS

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