Inorganic materials
Most of the techniques mentioned below are explained in the ScARF Science panel report. Many of these can be carried out in a number of laboratories in Scotland, with the important exception of a facility for (routine) organic residue analysis (ORA).
Pottery and ceramic building materials
The existing corpus of science-based data on pottery from the Wall and other Roman forts, which is quite small and site specific, would benefit from a fuller assessment. There is scope for wider data analysis such as that undertaken by Gillings which sought to identify local production (1991).
Petrography by thin-section analysis, coupled with elemental analysis should be used more extensively. Campbell and Jones have demonstrated that non-destructive X-ray fluorescence (XRF) analysis of samian works well, and rapidly, to determine its provenance, because the fabric is fine-textured and a chemical reference database for the workshops in Gaul is available (Jones and Campbell 2016). The same approach could be applied to other fine wares, but in the absence of reference databases the provenance information would be more limited. The same lack of comparative data also applies in the case of analysis by inductively coupled plasma-mass spectrometry (ICP – MS) (see Vannoorenberghe et al 2020), or neutron activation analysis (NAA) which gives a much fuller chemical characterisation.
The routine study of ORA on pottery from Roman sites to identify biomarkers can provide information about contents of the vessels, diet, subsistence and trade. For example, the study of mortaria using ORA by Cramp et al (2011), based on examples from Iron Age and Roman sites in England, could be extended to Scotland. The results pointed to a remarkably wide range of vessel contents. The scope for ORA, specifically gas chromatography-mass spectrometry (GC-MS) coupled with isotope analysis on other ceramics is appreciable (see Production and procurement).
Glass
There is no evidence for the primary production of glass from its raw materials in Britain at this time, and it is likely that it was either imported or glass cullet (broken, waste glass) was re-melted and recycled to make new objects. There are a small number of large-scale glass primary production centres in the Roman world (Freestone 2006; Jackson et al 2016). Scientific analysis of glass found along the Wall could be extremely valuable, using techniques such as portable X-Ray Fluorescence (p-XRF ideally under helium, to allow for lighter elements to be identified), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) for major and minor elements and by Laser Ablated-Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS) for trace and rare earth elements. Rare Earth Elements and isotopes may be able to identify the likely origin of the glass (see Jackson and Foster 2014 for discussion, Janssens 2013). As well as glass vessels from Wall forts there are also fragments of window glass found close to the line of the Wall for example at Falkirk (Keppie et al 1981) and a small amount of jewellery such as glass bangles, for example at Garnhall (Woolliscroft 2008, 168) and Rough Castle (Price 1988, 350). An analytical study could investigate the provenance of the different types of glass used to make these artefacts and compare the material from the Antonine Wall with Roman glass found elsewhere.
© Rediscovering the Antonine Wall
The evidence for Roman period glass working and melting is very sparse in Scotland, with finds from Camelon and possibly Newstead and Traprain Law (Price 2002, 90). It would be of particular interest to analyse vitreous material from the furnace near Camelon to determine the original provenance of the glass worked at this site and the extent of recycling or additions to the mix, such as the potential use of local minerals to colour or opacify the glass. A comparison with similar material found on Scottish Iron Age sites, such as Culduthel, might also yield some useful information (Bertini et al 2011).
All the methods above can also be applied to the analysis and understanding of enamel.
Metals
For copper alloys, a key issue is further exploration of alloying traditions in copper alloys, using elemental analysis, building on the conclusions of Dungworth (1997). Non-destructive characterisation of alloy types is a first step, with targeted destructive analysis for specific questions.
The question of primary metal resources versus recycling is a key one. It remains tricky to identify the origins of copper alloys, but a well-tried technique is the identification of the source of lead, using lead isotope analysis; this should be used more widely. Iron sourcing (from slag itself, or slag inclusions in metal) would help to clarify the extent of the use of local resources as opposed to imported ingots.
In terms of technology, the manufacture of iron artefacts is a topic of wider interest, which can be addressed using metallographic techniques (eg Photos-Jones 2016). These are not questions specific to the Antonine Wall, but demonstrating whether iron was produced locally or simply worked locally is an important question. Further analysis of slag assemblages would be valuable, including the use of techniques which could help to identify provenance and source through the application of typological and chemical analyses.
Stone
There has been limited work on the sourcing of decorated stone, such as the sandstone Distance Stones along the Wall, which has indicated, not surprisingly, the use of local quarries. There is a rich seam of specialised geological knowledge available on the sandstone sources/quarries in many parts of Scotland that could be exploited to assess whether, for example, neighbouring forts were accessing sandstone from the same or different quarries. However, actually pinpointing the precise outcrop/quarry used by a given fort by petrographic analysis would usually be more difficult to resolve; there is scope for further research into this, including community projects.
Emerging non-destructive techniques, including ED-XRF, pXRF, Raman Spectrometry and multispectral imaging, are being used to identify pigments originally applied to the Distance Stones (Campbell 2018; 2020). This will enable the physical and digital reproduction of colours, which will help to bring these monumental inscriptions back to life. Analysis of paint can be taken further: using methods such as x-ray diffraction (XRD), researchers can begin to identify mineral compounds rather than elemental composition. NAA and ICP-MS can also be used to identify organic elements which cannot be measured by XRF and can help us to investigate where the raw materials were coming from, and how pigments were prepared.
Organic materials
Sampling programmes to ensure the recovery of organic materials have long been applied during excavations, but they are not often targeted to support wider research agendas. Sampling strategies and sample types should be carefully considered in advance of excavation work, to ensure the widest possible systematic recovery of organic remains for scientific analysis. This includes samples for radiocarbon dating and Bayesian analysis to provide an age-depth model for the occupation and the use of the sites, situating the Roman presence and its impact within the wider Scottish Iron Age.
Systematic syntheses of the evidence for diet and food supply, where the evidence from multiple sites is combined and analysed, remain to be undertaken. Furthermore, soil sampling for geoarchaeological investigation is not standard practice. Micromorphology supported by soil chemistry can identify areas of activity, field systems and their management, as well as providing information on site formation processes more generally, and can be used to better understand the building materials of the Wall (see Soil-based materials). Analysis of lipid biomarkers can identify dung and excrement (eg Knights et al 1983). Plant opal phytolith analysis can help to locate sites or activity areas where peat, turf, plant and animal waste (including ash) could help with the identification of fuel ash residues, animal fodder or excrement and bedding materials.
In turn, this analytical method could also inform about the vegetation cover and thus characterise the areas where the turves for the Wall itself were sourced. Isotopic analysis of animal bone and teeth might be used to address the question of the use of droving – ie how far were animals being moved as part of the supply process (Stallibrass 2009). Identification of waterlogged material provides the opportunity to look for and study steroid lipid biomarkers, chronomid and other entomological remains, helping to elucidate the past environment, the use of space in structures and around sites, living conditions and animal management (eg Mackay et al 2020 for an Iron Age example), and advances in ancient DNA recovery and analysis means that sampling for sedaDNA should also be considered, to complement palynological work, in paleo-environmental reconstruction. In addition, near infrared spectrometry (NIRS) can aid in the study of local climatic changes.
Soil-based materials
The Antonine Wall is one of the largest turf structures in the world, and its construction has been evidenced in several sections excavated across the Wall, from the earliest systematic investigations by the Glasgow Archaeological Society to modern interventions as part of the planning system. However, this information has not been used to its full potential to understand the sourcing and the use of its soil-based building materials, mainly turves, but also earth and clay mixes. A general change in construction method between a complete turf construction in the area west of Watling Lodge and a clay-and-earthen core is generally noted (eg Keppie 1974). Investigations of individual sites in the eastern end of the Wall have demonstrated how complex this construction variant is, suggesting that either turf cheeks or clay-rich material was used for the facings (eg Breeze 1974; Keppie 1976, 68–72; Bailey 1995). More research into the details of the composition of the Wall construction and its materials should rely on geoarchaeological techniques such as micromorphology (ie thin-section analysis of these soil-based materials), combined with geochemical, mineralogical and organic analyses such as XRF and XRD, Particle Size Analysis and Phytholiths as well as Non-Pollen Palynomorphs (e.g. Romankiewicz et al 2020; 2022). This will help to characterise the composition of these materials, but can offer new understanding the complex process of construction, the sourcing of the specific material and strategic designs. It will also aid in the understanding of the decision-making process during the planning and building of the Wall as well as how it was maintained over time.
Non-invasive survey methods
Geophysical survey has long been used to investigate the Wall, focusing primarily on the search for associated civil settlements and the investigation of annexes (see Extramural activity and Annexes). While the recovery of evidence for both internal and extra-mural buildings has been limited because of the difficulties recognising structures based on post-holes, important contributions have been made in identifying new fortlets at Carlieth and Bonnyside, additional ditch systems to the north of forts at Balmuildy, Auchendavy and Mumrills, a new annexe enclosure at Carriden and external bathhouses at Auchendavy and possibly Castlecary (Hanson et al forthcoming). Some of the new geophysical survey techniques that have been developed on the continent in recent years should be applied to the Wall where possible.
More recently LiDAR survey of the Wall line has been undertaken by Historic Environment Scotland, the results of which have been analysed as part of a recent PhD at the University of Canterbury (Hannon 2018). Results suggest that the spatial resolution of the imagery is not sufficient to identify new fortlet sites or the remains of pits on the berm, but has provided more accurate measurements of both the overall length of the Wall and the spacing between associated structures (Hannon et al 2017; 2020).
Climate Science and Environmental analysis
Climate change is one of the fastest growing global threats and its impacts on the Wall should be considered as part of future research. Climate profiles for the sites along the Wall are essential to future proof decisions regarding its conservation and management, ensuring the survival of the Wall and associated sites and the archaeological information they hold. It is important to take into consideration that there will be slightly different climate trends between sites in the west and east of the monument. The Met Office can provide current climate data from the nearest climate stations and more recently, monthly, seasonal or annual data at 1km resolution. Climate projections for particular sites or areas might also be beneficial. Data from the Met Office and initiatives, such as the Hazard Mapping work, can provide information on a number of different proxies, such as rainfall, flooding and erosion, for recent changes and then future projections for 2060s–80s.
The soil-based studies described above (Soil-based materials) can also contribute to our understanding of how the Wall will be impacted by the changing climate. They can also inform us about the management strategies and adaptations that might help to preserve the important information that is contained within the monument for future research. A baseline study of the materials which comprise the Wall (eg, geochemical study of earth and turves) can provide a foundation level of knowledge on which to make these decisions. Using climate chambers to undertake accelerated weathering experiments, testing materials against high emission scenarios, could further augment this baseline.
The understanding of how water moves on and around the Wall and its associated sites is also important. We know from climate change studies that number of days of rain will increase, as will intense weather events, and hydrology modelling can help us understand the impact of this and aid management decisions. Mapping surface water flows will tell us where water comes from, how it moves across the site, where it pools and where erosion is taking place, and modelling this against rainfall projections will inform on how the surface flows might change through time. Mapping this and ground truthing will be non-invasive, through GIS mapping, geophysical survey techniques and field survey. Microwave moisture measurement may also be useful, but this has proven to be problematic if used alone. Studies of the construction of the Wall could also consider the flow of water through the rampart, and any potential impact it might have on its state of preservation in the future. Mapping of the moisture on site can also help to inform site infrastructure, such as the positioning of footpaths to features on site and sign boards, and the impact that people moving around a site can have on both upstanding and buried archaeological remains.
The Climate Vulnerability Index, an international approach to assessing the impact of climate change on World Heritage, was applied to the Antonine Wall in February 2022. The resulting report (Jones et al 2023) details some knowledge gaps for the Wall including those mentioned here in relation to better understanding of the turf structure and the movement of water.
Research issues
Inorganic materials
- Identify pottery, brick and tile production centres along the Wall.
- Use petrography and elemental analysis more extensively, working with specialists across Europe in establishing reference databases.
- Apply ORA on ceramics more widely in Scotland.
- Test for the possibility of local glass production and recycling using all available scientific techniques including a chemical study of vessels from Wall forts to assess the extent to which their characteristics match those established elsewhere.
- Characterise changing alloying traditions in copper alloys – this should be a standard approach in research and developer-funded projects.
- Sourcing of lead using isotope analysis as a standard approach.
- Investigation of possible iron sources, and particularly the question of local versus imported material.
- Available specialised geological knowledge could be exploited to assess whether neighbouring forts were accessing stone from the same or different quarries.
Organic materials
- Ensure that any excavations on sites with extensive waterlogged contexts are sufficiently well-funded to maximise the recovery of environmental remains (faunal, entomological, plant and sedaDNA, steroid lipid biomarkers – good results were recorded from the Iron Age site at Black Loch of Myrton, Dumfries and Galloway – Mackay et al 2020).
- Take every opportunity to record and fully analyse all building materials, particularly from anaerobic contexts using for example micromorphology, pollen and non-pollen palynomorph analysis, combined with chemical and mineral analyses, including XRF, XRD and mechanical and optical Granulometry.
Soil-based materials
- Undertake a systematic synthesis of the evidence for diet and food supply on the Wall.
- Undertake residue analysis on Roman pottery and stones in museums.
- Undertake chemical analysis to recover information about animals in forts on the Wall.
- Undertake isotopic analysis of animal bone/teeth to address the question of the long-distance supply of animals.
- Ensure that all excavations have a strategy for soil sampling with chronology, paleo-environmental reconstruction and geoarchaeological investigation in mind.
Non-invasive survey
- Consider the possibility of combining geophysical (including magnetic susceptibility measurement) and multi-element geochemical survey, backed up where advisable by biomarker analysis, to investigate potential activity areas around sites that have not suffered unduly from 19th–20th–century activity.
- Ensure the full publication of all geophysical surveys undertaken to date (see Hanson et al forthcoming).
- Consider the selective enhancement of the LiDAR coverage of the Wall in areas with the best preservation (eg Bar Hill, Croy Hill and Rough Castle/Tentfield Plantation) using greater spatial resolution.
Climate science and environmental analysis
- Undertake materials-based research into how the Wall and its associated sites will be impacted by environmental and climatic change, for example, earth and turf.
- Complete climate profiles across the Wall, using most recent climate projection data (for links see: eg https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-climate-averages/gcvwqum6h for current climate; https://ukclimateprojections-ui.metoffice.gov.uk/products; for recent climate trend and https://ukclimateprojections-ui.metoffice.gov.uk/products for climate projections).
- Undertake moisture mapping of sites along the Wall, such as that completed for Rough Castle (Blake forthcoming).