Historically, crannogs – dwellings located on natural, artificial, or semi-artificial islands near the shores of lakes and estuaries, which range in date from the Neolithic through to the 17th century – have been a bit of a mystery, with little known about their construction and usage. Recently, however, a number of new excavations and research projects have started to help fill in these knowledge gaps (see CA 325, 354, and 364). Furthering this research, an interdisciplinary team from universities across the UK and Norway have undertaken an ambitious project to apply a host of different biomolecular and mineralogical techniques to cores taken from lake settlements near crannogs located across Scotland and Ireland (and one in Wales) with the hope of better understanding these enigmatic sites. In this month’s ‘Science Notes’, we explore these techniques and see what results they have yielded.
This project revolves around a coring strategy based on the theory of ‘site-halos’. In effect, the area surrounding an archaeological site, while potentially not yielding any material evidence, still absorbs evidence of settlement activity through biomarkers left in the surrounding sediment or soil. While all sites probably have some sort of site-halo, those located around aquatic sites are more likely to be readily detectable because of anoxic (oxygen-free) conditions that help preserve both organic and inorganic materials. While it might seem that watery environments would wash away such evidence, palaeolimnological studies have consistently shown that in water-bodies with little mixing – which many crannogs are built on – sedimentation and absorption is highly localised. As the team points out: ‘this localisation is inconvenient for palaeolimnologists seeking general, lake-wide trends, but good for archaeologists, as it means that whatever gets washed off an adjacent island, promontory or platform, or through a pile-type structure, often remains close to the site, and can be preserved within nearby sediments.’
Thus, by coring and analysing the sediments adjacent to crannogs, we should be able to get an idea of what types of activity occurred during different periods of time. This has the added benefit that the site itself does not have to be cored or fully excavated in order to get high-precision data. To test this theory, the team studied the cores using different techniques.
For one, they tested if radiocarbon dating the sediment layers could provide more detailed site chronologies. They found that this was indeed possible, helping to provide a better idea of when particular crannogs were in use. Depending on factors such as how the crannog was constructed or how the site has eroded since, however, some layers of sediment surrounding the site may be lost or no longer be in strict chronological order (ABOVE), and thus some care must be taken with this approach. It might be that identifying concentrations of titanium – increases of which would indicate a human presence – through X-ray fluorescence (XRF) could be more useful, at least in determining construction and end dates.
In addition to dating, to understand the impacts of human settlement on these sites further, the team utilised a range of proxies to make inferences on their usage. For instance, by using microscopy to look for pollen in the sediment layers, the researchers were able to discern that crannog construction was often associated with local deforestation. Furthermore, high concentrations of pollen from herbs such as ribwort and bracken found at two of the crannogs suggests that meadows near to these sites were used to graze animals. They may also have been used for animal or human bedding and/or as roofing material.
The pollen results were further confirmed through plant sedaDNA (sedimentary ancient DNA) analysis, whereby plant DNA is extracted from the lake sediment samples. Meanwhile, using the same technique with a mammal primer showed that crannogs were associated, too, with an increase in the presence of domesticated animals such as cattle, sheep, pigs, and possibly goats, as well as wild red deer. Additionally, analyses using automated mineralogy to examine the composition of the cores helped reveal lots of shards of apatite in the occupation levels of some of the crannogs, which the team have interpreted as from fragments of animal bone from butchery waste.
The team tested many other techniques as well but, unfortunately, the breadth of this research is too wide to cover here. The full results, however, were recently published in Antiquity and are available at https://doi.org/10.15184/aqy.2022.70. In all, though, the results show that there are many ways in which coring sediments from the site-halo of crannogs can reveal a host of information as to activity that occurred on or near the sites during their occupation. It is hoped that further work in this area will help shed light on some of the ongoing questions around how crannogs were used throughout history. Moreover, while only crannogs were analysed in this study, the team emphasise that this methodology could be applied to any aquatic sites with little water-mixing, helping us better understand the chronology and use of islands, lakeshores, and marshes, from prehistory through to the post-medieval period.
TEXT: K Krakowka