Excavation

Date 13 June 2016 - 8 July 2016

Event ID 1025191

Category Recording

Type Excavation

Permalink http://canmore.org.uk/event/1025191

ND 4542 8688 (ND48NE 14) Excavation work continued, 13 June – 8 July 2016, at The Cairns (known by HES as ‘The Cairns of the Bu’), as part of on-going research on the Orcadian Iron Age. The work focused on the main area trench, c25 x 25m (Trench M), and a 10 x 10m area in the northern extension immediately to the NE of the main trench.

In 2016 a new zone of excavation was opened up between the existing trenches to create one extensive open-area. The new area was termed Trench Q and details of findings are given below.

Work continued on the inside of the broch (Structure A), and mainly concentrated on the SE quadrant largely within a well-defined area of the broch marked out by groups of orthostats that form partitions in the use of space. The removal of rubble on the N and W of the quadrant prior to

accessing occupation deposits revealed a finely built internal passageway, itself running off the main broch entrance. One side of this passage was constructed from large orthostatic panels while the other was a finely built coursed wall. This passageway had accessed two rooms set against the SE of the broch interior wall-face, and gaps in the orthostats defined

entrances into these spaces. The passage serves to further enhance the understanding of movement within the broch interior. The passageway and the rooms themselves formed the basis for the majority of the excavation work inside the broch this year. Within the passageway, occupation/floor

deposits were present across the surface and, in common with all sediments from inside the broch, these were excavated on a sample grid. Pottery and a fine copper alloy pin were among the small finds recovered.

In the SE zone of the broch interior a significant succession of deposits was observed ranging from dark organic carbon rich greasy layers to clean pale yellow clay. Significantly, the same detailed and quite clear stratification was present as had previously been witnessed in the floor/occupation deposits in the NE quadrant of the broch in 2015. It appears that similar, very good, preservation of floors is present across the whole of the E half of the broch thus far sampled.

Beyond the E zone of the broch, work continued in the western zone of the interior, and the last portion of rubble infill that had been deposited at the abandonment of the broch was finally excavated, revealing the full internal wall circumference of the broch upper levels. In the process, a doorway in the circuit leading into a very finely built, still fully roofed, extant intramural chamber, was discovered set in the western wall of the broch. Its entrance was similarly intact. This brings the total of substantial intramural features

in the broch wall to five. No excavation was undertaken within this chamber this season, but it has clearly been undisturbed since it was partly backfilled and sealed with rubble, sometime between the later 1st and 2nd centuries AD.

Work also took place on the outside of the broch, immediately against its outer wall and just to the N of the main broch entrance. Here, an area of rubble backfilled against the broch wall was sectioned to try to provide information with which to compare the dates of the backfilling episode of

the broch interior with that of the outside. Upon excavating the lower elements of this rubble, a remarkable deposit was encountered. A large, bucket-sized whalebone vessel carved from an entire vertebral bone had been deposited apparently immediately prior to the introduction of the rubble above.

Propped against the side of this vessel were two upright red deer antlers. The upper fill of the vessel contained a human mandible, and several loosely articulated animal bones (neonatal sheep). Finds of disarticulated or fragmentary human remains are a relatively common occurrence on

large Atlantic Iron Age sites and the concentration around the entrance area seems to have been a favoured zone for deposition of this kind of material, whether as foundation or decommissioning deposits. This particular, unusually complex, mixed deposit of artefacts and animal, and human remains, appears to represent something of an act of closure

marking the end of the broch immediately before it was shrouded in rubble externally. The human jaw, and a sample animal bone were radiocarbon dated and indicate that the person died around the same time that the deposition was made, sometime in the late 1st or 2nd century AD, very much in keeping with other C14 dates obtained for the end of the broch as an upstanding building. The dates also tend to support the idea that the broch was infilled internally and externally in the same single episode of wholesale decommissioning.

Immediately below the whalebone vessel deposit, a black, organic-rich deposit was encountered. This deposit was thick with limpet and winkle shells and replete with animal bone. This midden appears to emanate from the broch itself and the radiocarbon dates obtained from the deposits that sealed it suggest this is indeed material dating to immediately before the broch was abandoned, and possibly earlier.

It therefore appears that this midden will substantially assist the successful realisation of one of the key aims of the excavation of the broch: the detailed examination of a suite, or cycle, of production, processing, consumption and deposition, articulated across the broch interior, its floors, and its midden waste.

Additional work on the outside of the entrance area of the broch, also focused on the souterrain (Structure F), which post-dates the broch and which reused the broch entrance passage as the souterrain chamber. The fuller extent of the unroofed portion of the souterrain passage was tracked S, and found to form a c15m long structure. Meanwhile, work on the still-roofed portion, uncovered the entire run of surviving roof slabs and these were progressively recorded and lifted off. Three layers of major roof slabs were found to have been used to very soundly cap the souterrain passage.

The removal of these allowed a small amount of excavation inside the souterrain and on its deposits. The floors appeared to be simple and thin. A tiny amber bead fragment was recovered from one floor deposit during flotation of environmental samples. The floor/occupation deposits will be fully excavated next season. It was noted that, both the construction of the souterrain and the deposition of the whalebone vessel and human jaw appear to date from the same moment: immediately around the end of the broch, and may even have a shared significance in marking this seminal event. An antiquarian excavation (1901) in the entrance to the broch (later the souterrain chamber) found, amongst other things, two fragments of human bone.

In Trench M, the general aim was to gain more insight into the substantial metalworking that has previously been evidenced in this NE zone of the site. The remains of a clay furnace were fully excavated and found to be most likely involved in iron smelting. Slag and other residues indicated that there was heavy processing of iron ores under way. A second furnace was also identified and awaits full excavation.

As work progressed to reach earlier levels in Trench M, significant amounts of iron slag, bog ore, and so-called furnace bottoms, were encountered indicating that metalworking had been a hallmark of the N part of the site for a longer duration than the episode represented by deposits that have previously yielded considerable evidence of copper alloy

working including a spread of around 60 casting moulds that have been recovered in previous seasons.

Trench Q is the newly opened excavation area this year (c10 x 10m), positioned between the main broch trench and Trench M, and connecting both. Fairly substantial well-built wall-lines were identified in the western zone of this trench in particular. These were of double-faced character and in one case were surmounted by a smashed pottery vessel of a typical Middle Iron Age style. It seems likely that these walls represent elements of an extramural complex, or village, contemporary with the occupation of the broch.

Excavation work also continued on the so-called ‘Structure B area’, a complex of later Iron Age settlement post-dating the broch, and lying to the W of the broch, partly overlying the reduced broch wall-head, and formerly spilling over the infilled remains of the broch interior. The work identified a substantial entrance passageway leading into one of the B buildings, which had partly reused remnants of broch masonry to form on one sidewall of the passage. The base of the passageway constituted a set of shallow slab steps ascending in a southerly direction to give access to

Structure B1. The lowest base of the passage floor included four broken fragments of rotary quern which were found to refit together after they were recovered.

Archive: Orkney SMR and Orkney Museums Service (intended)

Funder: Orkney Islands Council and Archaeology Institute, University of the Highlands and Islands

Martin Carruthers - Archaeology Institute, Orkney College, UHI