Brochs, multi-storied roundhouses, are found across Scotland. They represent a sophisticated understanding of engineering with two thick outer walls separated by an air space and strengthened with reinforcing lintel slabs. A curious variation on this robust structure has been found in the Cairns, South Ronaldsay (Scotland).
     The building has walls 5 meters thick and an exterior diameter of 22 meters. The director of the dig, Martin Carruthers, explains that this is not the typical broch. "What we've got is this early broch-like structure - a dominating, big structure, with big, thick walls and a very large internal area. In essence, the features here are very conventional for a broch, but we've also got some other features, such as a series of tear-drop shaped cells built into the walls, that are not found in Orkney brochs. We can now see that these chambers were a weak point in the overall design. Their inclusion meant that sections of the roundhouse walls were unable to support the sheer weight of the masonry above them. These architectural 'problems' leave me wondering if we're dealing with a period of experimentation - an early attempt at broch-building from a time when the design and traditions surrounding broch-building hadn't quite been finalised or fixed." Martin notes, "I just think the whole thing couldn't have been very stable at a very high height."
     Pottery from the excavation indicates that it dates from approximately 2500 years BP, but more extensive dating is underway. The design is similar to brochs found in nearby Crosskirk (Scotland) which are believed to date from 3000 - 2000 years BP. The broch and other buildings at the site were probably used for centuries. At some point, this new construction rendered the walls so unstable that the broch collapsed onto itself. The remains of four Iron Age buildings have been excavated from on top of the original roundhouse. Archaeologists have found two buildings used for metal work, a living space and a souterrain, an underground chamber.
     Earlier this year, a roofed, underground passage was discovered that linked to the original roundhouse entrance. Apparently even after the collapse, the broch was used as an earth-house. The entrance was reinforced with two stone jambs that may have supported a door leading to the underground chamber. A bone pommel, perhaps from a sword, was found in the passage.      
     The metal-working structure (Building C) was in use approximately 2000 - 1500 years BP. Artifacts found include bronze moulds, and iron objects. There is a "door-knob" spear butt mould that is similar to ones discovered in Minehowe (Scotland). Their placement on the floor is something of a mystery. Martin explains, "What was this item, and the other iron objects, doing on the floor of Structure C? They must have been left on the floor at the end of the use of the building, but why is a difficult question to answer. It may be that they were old objects gathered together to be melted down and remade into something else. Alternatively, they may have been deliberately left on the floor of the workshop building as part of a ritual act of closure."
     The forges were fueled with peat that was found stacked outside and the heat was also used for drying grain. They may have also provided the fire that appears to have been deliberately set to close the buliding.
     The housing structure, Building B, may also have been ritually closed. A tiny, carved stone head, named the 'Cairns Character' was found last year. It appears to have been deliberately left along with other artifacts. The residential complex has yielded multiple stone hearths, pottery, stone tools and animal bones.
     Brochs in the Caithness region are unique in the way that their use evolved over the centuries. In most parts of Scotland, additional buildings were added around the broch, but it was left intact. In Caithness, the roundhouses were modified over time as additional construction was appended to them. Martin proposed that this may have been a way to retain a cultural connection to the original builders of the roundhouses.

Source: Orkneyjar (15 July 2010)