Broch remains before excavation
Diagram indicating possible phases of construction
A Broch is a high status house that reached its greatest development during the middle Iron Age. What now remains of the example at Thrumster is the base of such a building. It was first excavated during the early 19th century, one of the first of such excavations. Some 50 years later the remains were landscaped to form a garden feature. The southern section of the wall, which included the original broch entrance, was removed to build the summer house.
Sections of the monument were re-excavated in 2011 by a community based project run jointly by Yarrows Heritage Trust and AOC Archaeology Ltd. The left hand illustration is a representation of the broch structure as revealed by that project.
Excavation of the building interior demonstrated that it had been cleared out down to the bedrock during the 19th century and covered with soil to create a garden. A central flagpole (now gone) had been inserted into the bedrock. The wall top had been levelled and also covered in top soil.
This interpretation of the monument’s nature and history is tentative due the constraints imposed by limited surviving evidence. It would appear that the monument had a complex
history of construction, collapse, abandonment, modification and rebuilding extending from its construction about 300 BC through to 300 to 400 AD.
There is evidence of activity on the site as early as 400 to 450 BC before the monument was built. The ‘broch’ was built on a rocky ridge that had been quarried to supply blocky stone for the wall core structure. The core structure was then enclosed by a second wall constructed from thinner stone of a different type, brought into the site from a different source. The core structure and the outer wall were probably built about 300 BC. The monument appears to have suffered a partial collapse about 200 BC, which may have precipitated or occurred during a period of abandonment around that time.
A relatively short but intense burst of re-occupation activity occurred between 40 and 100 BC. This in turn was followed by a further long period of abandonment culminated by a re-occupation in the early Pictish period between 300 to 400 AD. There is evidence from pottery of activity continuing into the medieval period but no structural evidence was identified.
The diagram above indicates the complex nature of the structure due to its complex history of modification by different groups of its prehistoric occupiers. For example the entrance to the left of the diagram is not thought to be the original entrance. The wall is also complex having a wall-core of locally quarried stone and inner and outer linings of a different stone brought onto the site from a different quarry.The material coloured blue above is rubble that fills a gallery that may have extended around much of the original structure although the section under the steps would have been solid.
Finds of pottery, charred grain and other domestic items indicates that the building was, in essence, a house probably of a locally important person and their extended family.
We will never know what Thrumster Broch looked like, we can only make an educated guess based on excavation evidence both at Thrumster and other brochs. We know that not all brochs were exactly the same; like modern houses there were variations on a theme.
We think that Brochs had more than one floor, but wood does not survive well except when preserved in anaerobic conditions. Consequently we have no direct evidence of the wooden parts of the building, in particular we do not know how brochs were roofed.
The cutaway diagram below indicates the main features of a typical broch; it has been shown with a conical timber and thatch room with an access to the wall head but this is conjecture.
Diagram indicating the features defining a true broch
Thrumster Broch Excavation