Bullet impacts and built heritage damage 1640–1939
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Conflict damage to heritage has been thrust into the global spotlight during recent conflict in the Middle East. While the use of social media has heightened and enhanced public awareness of this ‘cultural terrorism’, the occurrence of this type of vandalism is not new. In fact, as this study demonstrates, evidence of the active targeting of sites, as well as collateral damage when heritage is caught in crossfire, is widely visible around Europe and further afield. Using a variety of case studies ranging from the 1640s to the 1930s, we illustrate and quantify the changing impact of ballistics on heritage buildings as weaponry and ammunition have increased in both energy and energy density potential. In the first instance, this study highlights the increasing threats to heritage in conflict areas. Second, it argues for the pressing need to quantify and map damage to the stonework in order to respond to these challenges.
rock surface hardness
geographical information system—ArcGIS indicates commercial software system
ultrasound pulse velocity
Armed warfare has wreaked havoc on the built environment for centuries. Major periods of conflict, such as the sacking of Athens by the Persians and the targeted destruction of major sanctuaries in 480 BC, provide clear historical precedents in the ancient world . Within the last century, Europe-wide destruction of dwellings during the world wars as part of bombings  may be compared with the dramatic deterioration of statues and buildings in the Angkor Wat compound during the 20-year Khmer Rouge-driven conflict (through post-conflict neglect as much as direct damage ). Such instances have left dramatic scarring on the built environment. While the extensive destruction of sites through the use of explosives has dominated current international headlines, relatively little is reported about the smaller scale destruction such as ballistic impacts (bullets) and shrapnel which can permanently scar and destabilise built heritage. Famous examples of this type of heritage damage include sites such as the Dublin Post Office (1916 Easter Rising impacts) and the bullet hole riddled walls of Budapest (1956 Hungarian Uprising), which are now commemorative sites in their own right. Conflict damage can therefore be associated with a changed status as a heritage site, turning a previously little-noticed site into a monument or providing an additional layer of ‘commemorative value’ to an existing heritage site. The commemorative role of heritage in post-conflict social reconstruction can be supportive, allowing the surviving population to rebuild their cultural identity, provided there is suitable management in place to facilitate reconciliation rather than encourage continued aggravation towards the ‘other side’ . However, the complexities of adding a new commemorative layer—i.e., the damage sustained during the conflict-to existing heritage such as monuments and places of worship require a more specific approach to the wider conversation about heritage and conflict: war-damaged heritage sites must instead be specifically targeted by conservation and restoration efforts to preserve both the heritage and, if possible, the new heritage in the form of conflict damage. The articulation and practice of a conservation strategy which is sensitive to these shifting concerns therefore requires a sound scientific understanding of the material damage caused by ballistic impacts over an extended period.
Developing such a strategy requires an interdisciplinary awareness of the multiple meanings of heritage and conflict. In the first instance, conflict damage can be used as an excuse to facilitate widespread clearing of heritage sites. For example, in the years after World War II the city of Bristol saw the war damage as a ‘golden opportunity’ to facilitate the introduction of large scale infrastructure, as journalist Max Barnes in the Evening Post (25th September 1942) argued: “Probably you think there are too many arty-crafties and architectural windbags coming down to Bristol advising the Corporation to waste your rates on preserving tatty old disused church towers.” The desired destruction of the majority of religious buildings, including as churches and chapels, in favour of shopping centres was met with opposition at the time. As a reader of the Bristol Evening Post (18th June 1946) lamented: “It is sure a tragedy… that this historic landmark [Broadmead Chapel] should fall a victim to the march of progress. Progress, how many crimes have been perpetrated in thy name?” Even such brief exchanges suggest that heritage remains in need of a defender post-conflict as much as it is during the conflict, especially when it has sustained significant conflict damage. Therefore conservation strategies for conflict damage on heritage should consider both  prevention of further damage through long-term deterioration and  prevention of reckless replacement of heritage. This includes prevention of removal of original material when the damage does not threaten overall structure stability. Careful conservation of these sites therefore requires a quantitative knowledge of the physical damage inflicted by ballistics, within the context of the date of impact and the weaponry used, which can be applied alongside qualitative understandings of shifting cultural value.
Damage to heritage in conflict zones can be inflicted either when the heritage is simply standing in the way of a conflict, getting caught in the crossfire, or in a more targeted way such as vandalism, which includes any destruction of heritage that can be denounced as barbarous, ignorant, or inartistic treatment . This type of destruction contrasts with iconoclasm, which refers to the opposition to, and destruction of, religious images and sites as an act to overthrow the religious beliefs of others and physically and metaphorically dismiss them as fallacious or superstitious . In recent years, ideology-driven destruction of heritage during conflict has been particularly associated with the Middle East and the activities of Daesh/So-Called IS, and the rise of what is now termed ‘cultural terrorism’ [6, 7]. The coming together of physical damage and social media has arguably increased the profile of heritage sites in conflict areas [8, 9]. What is of particular concern in context of this increasing targeting of heritage, as this research illustrates, is that the tools with which this destruction can be inflicted are increasing in strength and availability. Whereas the results discussed in Case Study 1 show that the musket balls used in the 17th century were relatively non-destructive to wider structural stability, the Mauser guns used in the 20th century have (Case Study 4) left a network of fractures throughout the stone that threaten not only the direct impact site but also the wider stone ledges. This accelerating potential to inflict damage, when considered alongside the sort of ideologically-driven destruction outlined very briefly above, requires a careful analysis of the impact of ballistics on stone surfaces. In this research we explore this increasing damage curve by contrasting historic ballistic impacts.
To assess this increasing damage inflicted on heritage by ballistics we present four very different case studies that all share a common scarring by ballistics sustained during conflict and/or created by vandalism associated with conflict. These illustrate the wide ranging occurrence of this type of damage and highlights the complexities that are created by the high-velocity/high-energy impact of a bullet upon a stone surface. Despite the prevalence of this type of damage in our built environment, relatively little is known about the short- and long-term implications of ballistic impacts . What is even more concerning is the rapid pace of development of ammunition and the ever-increasing risk it poses to heritage. To highlight this increasingly-destructive nature of ballistics, and the associated concerns for heritage conservation, the case studies here have been placed in chronological order: (1) Accidental damage in the Civil War in Great Britain and Ireland (1642–1651) (Powick, Gloucestershire), (2) Ideology-driven damage in the Civil War in Great Britain and Ireland (1642–1651) (Oxford, Oxfordshire) (3) Colonialism and vandalism during the Lalangibalele uprising (1873–1874) in South Africa (uKlahamba Drakensberg); and (4) Spanish Civil War (1936–1939) in Madrid. We utilise the Case Studies 1, 2 and 4 to highlight quantification of the material damage incurred during conflict. Due to the sensitive nature of the site it was not possible to take measurements of surface deterioration for Case Study 3, but the variability in angle at which the rock art was shot at is used here to illustrate the complex nature of ballistic impacts as well as the progression from musket impacts (case studies 1 and 2) to matchlock rifles.
Case studies 1 and 2: civil war in Great Britain; ideology-driven and collateral damage (1642–1651)
While the current scale and global awareness of destruction of heritage in the Middle East is unprecedented, it is by no means the first occurrence of ideology-driven targeted destruction of buildings and objects. Some authors assume the French Revolution was a milestone in the history of art destruction , but there are numerous instances of ideology-driven damage throughout history. These not only include the above-discussed iconoclasm, but also “spolia”, which includes the destruction, even of entire buildings, often with a symbolic purpose of destruction of the people who built them. This has been commonplace in Europe since Roman times . Iconoclasm and “spolia” therefore share an ideology-driven destructive purpose, but iconoclasm is eminently focused on the religious resonances of the destructive act, while “spolia” includes a more general societal attack. For instance, during the Civil War in Great Britain and Ireland, active targeting of religious sites (in particular those elements which were most heavily contested such as images of saints and altar rails ) by Parliamentarian groups as well as local pressure groups was part and parcel of the wider conflict. In each instance, the historical relevance of the heritage is deeply connected with the destruction itself, with the ballistic impacts providing an essential element of the wider narrative.
In this example, religious artefacts destruction has become not only a way of destroying religious artefacts (iconoclasm), but also a way of expressing the symbolic destruction of a previous regime (spolia). For example, Budd  notes that the deliberate destruction of the Cheapside Cross in London (also during the Civil Wars of the 1640s) was as much an act of popular religious expression as a symbolic statement about the allegiance of London to the reforming cause. The religious ideology behind the act is so entwined with political allegiance that the two are virtually inseparable, as was the case during the Civil War . In these instances, damage to heritage gains further historical relevance, and makes a strong case for preservation of the damaged sites. Such targeted destruction was not restricted to the London area, but took place wherever Parliamentarians felt emboldened either through local pressure groups or the presence of the Parliamentarian army. In the case of Powick Church (Case Study 1), the site became collateral damage as Royalists troops using the elevated position as a look out were shot at by Parliamentarian troops, which has left a collection of musket ball impacts on the tower. The damage to the second site (Case Study 2) was far more deliberate, as the statue of St. Mary was targeted by the Parliamentarian troops to eradicate doctrinally-objectionable religious imagery, leaving it pockmarked with musket ball impacts and removing the nose altogether. Once again, the survival of such damage into the present day and their historical resonances pose important challenges to heritage conservation well beyond qualitative understanding.
Case study 1: Powick Church, Gloucestershire, UK
Rock surface hardness
As several studies have demonstrated [18, 19, 20, 21], RSH can be used as a key-indicator of the degree of weathering of a surface. In this study, an Equotip 3 with a D-type probe was used to map variations in weakening of the stone surface. This equipment was originally developed for the testing of metals , but is now used in both natural settings [23, 24] and the built environment . The surface hardness is measured through rebound of a 3 mm diameter spherical tungsten carbide test tip against the rock surface. This tip is mounted in an impact body and impacts under spring force against the test surface from which it rebounds . The velocity before impact (V,) and after impact (V2) are measured automatically and displayed as a ratio (V2/V, × 1000) which is denoted by the unit ‘L’, or Leeb unit . The nine blocks were each subdivided into 50 measurement points, noting distance from nearest bullet impact.
Surface hardness interpolation (Kriging)
ArcGIS (ArcMap 10.4) was used to map the most likely distribution of surface hardness. All measurements were plotted on a georeferenced image of the individual building block, which was then used to carry out Kriging ordinary spherical interpolation of most likely surface hardness measurement distribution. All test blocks were plotted both using a general range that covered all measurements (100–400 Leeb hardness values), to facilitate cross-block comparison.
However, when ballistic impacts are closely spaced together there does appear to be a more focussed deterioration, as demonstrated in block 6 analysis (Fig. 4c, d). As shown in Fig. 4d, which was plotted on a limited Leeb hardness scale to reflect variations within the individual block, the areas immediately surrounding the large impacts have deteriorated further (Leeb values ranging from 243 to 290) than the areas towards the bottom of the block (Leeb values ranging from 280 to 330). This leads to the hypothesis that low-impact ballistic damage in principle does not cause extensive weakening of the surface; in fact, a singular impact could exhibit strengthening rather than weakening of the surface, though this is measured through about 350 years of exposure, but that clusters of low-impact damage do lead to enhanced deterioration of structural strength of the block and therefore need to be assessed as a potential conservation risk.
Case study 2: ideology-driven damaging of St. Mary the Virgin, Oxford, UK
In this case study, deliberate damage to build heritage-representing ideology-driven “cultural terrorism” and its resultant damage by the Parliamentarian troops outlined at the beginning of “Case studies 1 and 2: civil war in Great Britain; ideology-driven and collateral damage (1642–1651)”—is contrasted with the unintentional damage to heritage caught in crossfire illustrated in the Case Study 1. This case study investigates the deliberate damage to St. Mary the Virgin on the High Street in Oxford, which is the University Church of the University of Oxford. In contrast with Case Study 1, these impacts on the limestone statue have not been left exposed but instead have been repaired using lime mortar. This case study therefore also illustrates problems in accurately assessing damage when infill of, or other ‘restorative work’ on, the impact area has taken place.
As in Case Study 1, surface hardness was used to determine relative deterioration of the surface. This was quantified using the same Equotip 3 with D-type probe. Sampling was directed by the features of the statue, e.g. chin, nose, crown, neck, etc. (Fig. 7e), and with notes taken on sections where supposed ballistic impacts were located (Fig. 7d). Where an impact had taken place the area directly adjacent to the repairs was measured, rather than on the infill of the indentation left by the ballistic, which would merely have measured the strength of the lime mortar rather than the damage to stonework. The mean hardness value, presented in the figures, was calculated using 10 repetitions of impact measurements at each sample site, following previously established procedure of using multiple measurements in one surface area to offset outliers [24, 40, 41].
The clustering of the impacted areas of Group 2 (mean Leeb value 246.36), which are in sections of the statue comparable to those in Group 3 (mean Leeb value 260.75), indicates that an overall deterioration of surface structure where a matchlock musket ball has hit at this site led to a reduction in mean Leeb value of 5.52%. The standard deviation does not vary noticeably between the two groups, respectively 51.06 (Group 2) and 51.71 (Group 3), indicating that difference between the two groups is based on a general lowering of the Leeb value where impacts have taken place, rather than an increase in measurement variability.
Difficulties in accurately assessing the long-term consequences of these ballistic impacts is exacerbated by the presence of the repairs carried out in 1865; the addition of lime mortar to the cavities in limestone of the statue obscure the impact cavity and prevent measurements of the impact surface. Furthermore, later addition of alien material has been noted to accelerate deterioration in heritage structures (e.g. ), which needs to be accounted for when assessing the relative impact of ballistics on surface deterioration. As this limestone statue was repaired using lime mortar it is assumed here that the elastic modulus and moisture retention behaviour was compatible and that therefore the reduction in surface strength can be contributed to the ballistic impacts. However, experimental research is needed to conclusively quantify the influence of alien material introduction on impact site deterioration.
Colonialism and cultural vandalism
The erosion of cultural pride under a colonial regime as a country-wide phenomenon has been remarked upon by scholars such as Taruvinga and Ndoro , as indigenous sites and art often faced neglect if not outright vandalism within colonial regimes. The disregard for indigenous culture during periods of colonial rule as well as the deliberate destruction of culture to establish dominance are themes that resonate in conflicts throughout history in what Bevan considers “calculated acts of cultural annihilation” . In particular, in times of conflict site security and heritage-protective legislation can be either ineffective or unenforced; this is illustrated by the case study presented here, where boredom of troops superseded any awareness of the cultural importance of the sites they targeted for sport. The protection of indigenous culture in particular can be at risk when an external force is in conflict with the local population, increasing the risk of vandalism and neglect. In this case study, we explore vandalism during the 19th century, when weaponry and ammunition had evolved from the matchlock muskets discussed in case studies 1 and 2 to the more sophisticated percussion lock rifle.
Case study 3: damage to San rock art, Giant’s Castle Main Cave, Drakensberg South Africa
20th Century conflict
The case study discussed here, the School of Medicine of the Complutense University of Madrid, represents not only this 20th century damage and its associated increase in ballistic impact power, but also provides a very good baseline for impact measurements; this war damage was inflicted very soon after the completion of the building. Therefore, ballistic damage was not superimposed to any previous weathering process and any differences in deterioration behaviour can therefore be attributed to ballistic damage. This is in contrast with the previous case studies where the sites had been created centuries before ballistic impacts hit their surfaces, and where weathering inheritance might alter the long-term response of the stone to ballistic impacts [10, 52].
Case study 4: Complutense University of Madrid
Recent conflicts tend to involve a wider variety of armament and ammunition, thereby increasing the variability and complexity of contemporary ballistic damage. This case study displays a mixture of impacts coming from bullet impacts (mainly from Mauser M1893 rifles, though it is possible that other rifles may have been added on an impromptu basis to the arsenal of the fighters) and shrapnel impacts from nearby bomb explosions. Shrapnel fragments include lead balls as well as steel fragments of different shapes and sizes. This contrasts with the previous case studies in which all projectiles impacting on stone came from the same source and were similar in size. Therefore, a key issue at this site is the relationship between impact size and resulting damage, which is quantified here.
Three damaged window ledges were selected to characterize the mechanical properties of the areas affected by impacts. Ultrasound Pulse Velocity (UPV) was measured with a CNS electronics Pundit portable ultrasonic test equipment, which can detect a reduction in stone strength even when no deterioration is visible at surface level . While UPV investigations were attempted at case studies 1 and 2, it was not possible to obtain measurements on those sites due to interference by metal reinforcement structures within the stonework, such as pinning, which interfered with the signal. It was, however, successfully applied in this case study.
Leeb rebound hardness was measured using similar methodology to the previous case studies (Equotip 3 with D-type probe). In addition to measurements on the damaged ledges 30 measurements were taken on an undamaged window ledge to obtain baseline values of these properties.
The size of 30 impacts identified in the damaged areas was recorded, with size of impact calculated as an ellipsoid according to longest horizontal and vertical axis. UPV and surface hardness (Leeb) measurements were taken inside each impact to compare the values with the average of undamaged ledge and test how the size of the impact affected compaction and internal damage. Measurements were taken in a 100 × 20 cm area, so different sizes of impacts were measured. Measurements were taken using a grid with a spacing of 6 cm (horizontal) and 3 cm (vertical). UPV was measured in each point of the grid with 1 MHz transducers, plasticine as contact medium, and a constant spacing between transducers of 3 cm. Leeb hardness was measured as the average of three impacts for each point of the grid.
In smaller impacts the surface exhibits similar compaction patterns to those observed in the older, lower force impacts demonstrated in Case Studies 1 and 2, strengthening the assumption that smaller impacts are caused by lead shrapnel similar to musket ammunition. Therefore, this case study illustrates the differences shown in Fig. 5 (Case Study 1) between energy density and dispersal of rifle impacts in which damage penetrates deeper in the stone, and “low impact” lead bullets in which the majority of the damage associated with the impact is released on the surface. This stress release at surface level is likely to exploit pre-existing weaknesses, such as bedding planes, to dissipate outwards. This follows the principles shown by Barauskas and Abraitiene  who mapped surface deformation around the impact site in multilayer fabrics.
Unlike the results reported in case studies 1 and 2, where damage appeared to be restricted to the surface and near-surface in the area immediately surrounding the impact zone, stress generated by the Madrid impacts travels through the surface and causes deterioration away from the initial impact zone. This fundamental change in damage pattern, causing wider spread subsurface structural damage through fracture network development, indicates the changing nature of the deterioration threat to heritage that more recent ballistic impacts pose. These fracture networks can not only deteriorate the strength of the stone at time of impact but can also be exploited by weathering processes for more rapid deterioration of the stone on the medium- and long-term. While historic low-energy impacts, such as those illustrated in case studies 1 and 2, can exhibit very little long-term deterioration of the wider stone block and give little cause for concern we need to fundamentally change the way we approach conservation of ballistic impacts to reflect the energy and penetrative nature of contemporary bullet impacts.
These case studies illustrate a temporal range of impacts, namely the 17th, 19th and 20th centuries, which represent the ongoing development of ballistic weaponry. In particular, the contrast between the rounded musket balls (Case Studies 1 and 2) and the more modern weaponry of the 20th century highlights the increasing intensity of the ballistic impacts. In addition to this, modern warfare is characterised by a more extensive mixture of coexisting weaponry. Where previously some damage or even compaction of the surface is associated with musket ball impacts, Case Study 4 has revealed the resonating impact further into the stone, creating far more complicated fracture networks and energy dissipation than might be visible on the surface. This increasingly penetrating nature of ballistic missiles, both in terms of the bullets themselves and the weaponry used to shoot them, is a cause for grave concern for the future conservation of damaged heritage in conflict areas; if ballistics continue to increase in strength both in terms of energy and energy density at point of impact as well as increasingly efficient penetration of a material, it will be increasingly difficult to stabilise heritage post-conflict.
Targeted and incidental (cross-fire) destruction of culture is not a new phenomenon, in fact ballistic scars can be found on multiple continents ranging many conflicts and spanning centuries, as illustrated by our case studies. These impacts require careful consideration in conservation strategies, in terms of the relative strength of the impact (Case Studies 1 through 4), the clustering of impacts (Case Studies 1 and 4), and the angle of impact (Case Study 3).
The enhanced threat to built cultural heritage in contemporary conflicts lies in the increasingly-destructive penetrative of nature of ballistics. While Case Study 1 showed relative strengthening of the surface in singular impact sites (but not in clustered impact sites), the far more destructive artillery of Case Study 4 showed a much more noticeable deterioration throughout the stonework. This increasing subsurface damage beyond the immediate impact zone needs to be taken into account when assessing damage to both historic and contemporary sites. In addition, these measurements can be seen as a warning of the continuing development of weaponry and the effect that ballistics will have on heritage stonework in future conflicts.
In this light, it is therefore important that the scientific community continues to explore the impact of ballistics on stone surfaces, building on the work presented here to quantify the impact of conflict on stonework strength and deterioration. While it might seem obvious that older impacts from lower-strength artillery create less damage, this research has identified the complexities associated with multiple impacts and has also provided the first quantification of ballistic impacts on historic stonework.
As illustrated by the case studies, the impact of ballistics on build heritage is of increasing concern; the development of artillery since the 1600 s shows the increasingly destructive trajectory of ballistics development. To fully understand the threat that historic as well as contemporary ballistic impacts pose to build heritage we therefore need to take into account when the conflict took place, e.g. how variable and penetrative the ballistics were at the time, and use this knowledge to extrapolate the likely presence of subsurface deterioration of the stone which is not visible from the surface. This study presents the first quantification of the impact of ballistics on historic stonework and shows the accelerating damage curve associated with the development of artillery over the centuries.
LM collected the data for case studies 1, 2 and 3 and wrote the manuscript. MG-H collected the data for case study 4 and contributed to the manuscript. Both authors read and approved the final manuscript.
The authors are very grateful for the goodwill of Prof John Lewin and the Powick Church Trust, as well as St Mary the Virgin and their restoration employers for facilitating access to the premises. We thank Dr Laura López and Geomateriales 2 S2013/MIT-2914 for assistance with GIS analysis and support for Case Study 4. We also want to thank Prof Heather Viles for the loan of laboratory equipment used to carry out this research. We are grateful for the assistance of Dr Mark Williams in improving the historical narrative of this manuscript. Finally, we want to thank two anonymous reviewers whose helpful suggestions and comments were very valuable in improving this manuscript.
To the best of the author’s knowledge there are no competing interests associated with this research.
Availability of data and resources
All data is available directly from the authors on request. Please contact the corresponding author for access.
Ethics approval and consent to participate
This research was carried out under Leverhulme Trust Research Grant RPG-2017-408.
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