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 ballis‑ tics 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. Introduction own right. Conflict damage can therefore be associated Armed warfare has wreaked havoc on the built environ- with a changed status as a heritage site, turning a previ- ment for centuries. Major periods of conflict, such as ously little-noticed site into a monument or providing the sacking of Athens by the Persians and the targeted an additional layer of ‘commemorative value’ to an exist- destruction of major sanctuaries in 480 BC, provide clear ing heritage site. The commemorative role of heritage in historical precedents in the ancient world . Within the post-conflict social reconstruction can be supportive, last century, Europe-wide destruction of dwellings during allowing the surviving population to rebuild their cultural the world wars as part of bombings  may be compared identity, provided there is suitable management in place with the dramatic deterioration of statues and buildings to facilitate reconciliation rather than encourage contin- in the Angkor Wat compound during the 20-year Khmer ued aggravation towards the ‘other side’ . However, the Rouge-driven conflict (through post-conflict neglect as complexities of adding a new commemorative layer—i.e., much as direct damage ). Such instances have left dra- the damage sustained during the conflict-to existing herit - matic scarring on the built environment. While the exten- age such as monuments and places of worship require a sive destruction of sites through the use of explosives has more specific approach to the wider conversation about dominated current international headlines, relatively lit- heritage and conflict: war-damaged heritage sites must tle is reported about the smaller scale destruction such as instead be specifically targeted by conservation and res - ballistic impacts (bullets) and shrapnel which can perma- toration efforts to preserve both the heritage and, if pos - nently scar and destabilise built heritage. Famous exam- sible, the new heritage in the form of conflict damage. The ples of this type of heritage damage include sites such as articulation and practice of a conservation strategy which the Dublin Post Office (1916 Easter Rising impacts) and is sensitive to these shifting concerns therefore requires the bullet hole riddled walls of Budapest (1956 Hungarian a sound scientific understanding of the material damage Uprising), which are now commemorative sites in their caused by ballistic impacts over an extended period. Developing such a strategy requires an interdisciplinary awareness of the multiple meanings of heritage and con- *Correspondence: email@example.com flict. In the first instance, conflict damage can be used as Department of Geography and Environmental Management, University an excuse to facilitate widespread clearing of heritage sites. of the West of England, Frenchay Campus, Coldharbour Lane, Bristol BS16 1QY, UK For example, in the years after World War II the city of Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/ publi cdoma in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 2 of 16 Bristol saw the war damage as a ‘golden opportunity’ to the stone that threaten not only the direct impact site but facilitate the introduction of large scale infrastructure, as also the wider stone ledges. This accelerating potential to journalist Max Barnes in the Evening Post (25th Septem- inflict damage, when considered alongside the sort of ide - ber 1942) argued: “Probably you think there are too many ologically-driven destruction outlined very briefly above, arty-crafties and architectural windbags coming down to requires a careful analysis of the impact of ballistics on Bristol advising the Corporation to waste your rates on stone surfaces. In this research we explore this increasing preserving tatty old disused church towers.” The desired damage curve by contrasting historic ballistic impacts. destruction of the majority of religious buildings, includ- To assess this increasing damage inflicted on heritage by ing as churches and chapels, in favour of shopping centres ballistics we present four very different case studies that was met with opposition at the time. As a reader of the all share a common scarring by ballistics sustained dur- Bristol Evening Post (18th June 1946) lamented: “It is sure a ing conflict and/or created by vandalism associated with tragedy… that this historic landmark [Broadmead Chapel] conflict. These illustrate the wide ranging occurrence of should fall a victim to the march of progress. Progress, this type of damage and highlights the complexities that how many crimes have been perpetrated in thy name?” are created by the high-velocity/high-energy impact of a Even such brief exchanges suggest that heritage remains in bullet upon a stone surface. Despite the prevalence of this need of a defender post-conflict as much as it is during the type of damage in our built environment, relatively little conflict, especially when it has sustained significant con - is known about the short- and long-term implications flict damage. Therefore conservation strategies for conflict of ballistic impacts . What is even more concern- damage on heritage should consider both  prevention ing is the rapid pace of development of ammunition and of further damage through long-term deterioration and the ever-increasing risk it poses to heritage. To highlight  prevention of reckless replacement of heritage. This this increasingly-destructive nature of ballistics, and the includes prevention of removal of original material when associated concerns for heritage conservation, the case the damage does not threaten overall structure stability. studies here have been placed in chronological order: Careful conservation of these sites therefore requires a (1) Accidental damage in the Civil War in Great Britain quantitative knowledge of the physical damage inflicted by and Ireland (1642–1651) (Powick, Gloucestershire), (2) ballistics, within the context of the date of impact and the Ideology-driven damage in the Civil War in Great Britain weaponry used, which can be applied alongside qualitative and Ireland (1642–1651) (Oxford, Oxfordshire) (3) Colo- understandings of shifting cultural value. nialism and vandalism during the Lalangibalele uprising Damage to heritage in conflict zones can be inflicted (1873–1874) in South Africa (uKlahamba Drakensberg); either when the heritage is simply standing in the way and (4) Spanish Civil War (1936–1939) in Madrid. We uti- of a conflict, getting caught in the crossfire, or in a more lise the Case Studies 1, 2 and 4 to highlight quantification targeted way such as vandalism, which includes any of the material damage incurred during conflict. Due to destruction of heritage that can be denounced as barba- the sensitive nature of the site it was not possible to take rous, ignorant, or inartistic treatment . This type of measurements of surface deterioration for Case Study 3, destruction contrasts with iconoclasm, which refers to but the variability in angle at which the rock art was shot the opposition to, and destruction of, religious images and at is used here to illustrate the complex nature of ballistic sites as an act to overthrow the religious beliefs of others impacts as well as the progression from musket impacts and physically and metaphorically dismiss them as falla- (case studies 1 and 2) to matchlock rifles. cious or superstitious . In recent years, ideology-driven destruction of heritage during conflict has been particu - Case studies 1 and 2: civil war in Great Britain; larly associated with the Middle East and the activities of ideology‑driven and collateral damage (1642– Daesh/So-Called IS, and the rise of what is now termed 1651) ‘cultural terrorism’ [6, 7]. The coming together of physical While the current scale and global awareness of destruc- damage and social media has arguably increased the pro- tion of heritage in the Middle East is unprecedented, it file of heritage sites in conflict areas [8 , 9]. What is of par- is by no means the first occurrence of ideology-driven ticular concern in context of this increasing targeting of targeted destruction of buildings and objects. Some heritage, as this research illustrates, is that the tools with authors assume the French Revolution was a milestone which this destruction can be inflicted are increasing in in the history of art destruction , but there are numer- strength and availability. Whereas the results discussed in ous instances of ideology-driven damage throughout Case Study 1 show that the musket balls used in the 17th history. These not only include the above-discussed icon - century were relatively non-destructive to wider struc- oclasm, but also “spolia”, which includes the destruction, tural stability, the Mauser guns used in the 20th century even of entire buildings, often with a symbolic purpose have (Case Study 4) left a network of fractures throughout of destruction of the people who built them. This has Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 3 of 16 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 Parliamentar- ian groups as well as local pressure groups was part and parcel of the wider conflict. In each instance, the histori - cal 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 politi- cal allegiance that the two are virtually inseparable, as was the case during the Civil War . In these instances, dam- Fig. 1 Powick Church tower wall damaged by musket‑ball shots age 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, Scottish troops exploited the elevated position of the church but took place wherever Parliamentarians felt emboldened to observe the surrounding countryside, but were discour- either through local pressure groups or the presence of the aged from continuing to do so by musket-ball shots fired Parliamentarian army. In the case of Powick Church (Case by the approaching Parliamentarian troops (  p. 75–78) Study 1), the site became collateral damage as Royalists using either a matchlock or a flintlock musket . Figure 1 troops using the elevated position as a look out were shot shows an overview of the affected wall. Though not clearly at by Parliamentarian troops, which has left a collection of visible in this image, the majority of the musket-ball pock- musket ball impacts on the tower. The damage to the sec - marks are located at the height of the ladder and above. ond site (Case Study 2) was far more deliberate, as the statue A closer look at these pockmarks shows the relatively of St. Mary was targeted by the Parliamentarian troops to limited damage 17th century ammunition inflicted eradicate doctrinally-objectionable religious imagery, leav- on sandstone (see Fig. 2); the indentures of the musket ing it pockmarked with musket ball impacts and removing balls are visible as a concavity in the stone surface with a the nose altogether. Once again, the survival of such dam- deeper direct impact centre surrounded by a more shal- age into the present day and their historical resonances pose low removal of materials at the near-surface. important challenges to heritage conservation well beyond To understand what effect ballistic impacts from the qualitative understanding. 17th century have on the deterioration of the stone, rock surface hardness (RSH) measurement surveys were car- Case study 1: Powick Church, Gloucestershire, UK ried out across nine impacted building blocks (see Fig. 3). St. Peter’s Church is situated about two miles south-west These blocks represent a range of impact densities, from of Worcester (Gloucestershire, UK) in Powick. Parts of the a single impact on a block (block 8) to six impacts within building date back as far as the 12th century though the short distances of each other (block 6). church in its current form was largely established in the 14th and 15th century, including the tower referred to in this study . The objects of interest for this study are the bullet Methodology impacts on the tower, a result of the fighting on the advance Rock surface hardness As several studies have demon- of Parliamentary troops on 3 September 1651. Royalist strated [18–21], RSH can be used as a key-indicator of the Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 4 of 16 Fig. 2 a Ballistic impacts on the tower of St Peter’s Church in Powick; b close up of ballistic impacts shown in (a) surface hardness. All measurements were plotted on a geo- referenced image of the individual building block, which was then used to carry out Kriging ordinary spherical inter- polation of most likely surface hardness measurement dis- tribution. All test blocks were plotted both using a general range that covered all measurements (100–400 Leeb hard- ness values), to facilitate cross-block comparison. Results For this study, three of the blocks were selected for fur- ther analysis, representing low number of impacts (block 3), mixed small and large impacts (block 5) and high den- sity of large impacts (block 6) to illustrate spatial patterns in surface hardness associated with ballistic impacts. Fig- ure 4 shows the results for all three blocks. Fig. 3 Measured sites on Powick Church, including case study blocks As illustrated by Fig. 4a, relatively little variation in 3, 5 and 6 in the centre of the general impacted area surface hardness measurements is exhibited on block 3, which received only three large ballistic impacts. In fact, degree of weathering of a surface. In this study, an Equotip the areas directly surrounding the impacts appear a lit- 3 with a D-type probe was used to map variations in weak- tle more robust than the areas further removed from the ening of the stone surface. This equipment was originally impact. The majority of the deterioration appears to have developed for the testing of metals , but is now used in taken place towards the bottom-left of the block, which both natural settings [23, 24] and the built environment . could be associated with deterioration patterns often The surface hardness is measured through rebound of a 3 mm observed in sandstone building stone based on mois- diameter spherical tungsten carbide test tip against the rock ture movement through the blocks  at the intersec- surface. This tip is mounted in an impact body and impacts tion between porous stone and mortar . The more under spring force against the test surface from which it remarkable observation is that the areas where the bul- rebounds . The velocity before impact (V ,) and after lets have impacted appear to have strengthened, rather impact (V2) are measured automatically and displayed as a than weakened. This same pattern is repeated at block 5, ratio (V2/V, × 1000) which is denoted by the unit ‘L, or L ’ eeb where areas of most severe weakening are outside of the unit . The nine blocks were each subdivided into 50 meas - impact zones. It is likely that this is a function of the flex - urement points, noting distance from nearest bullet impact. ural strength of the sandstone and the nature of a mus- ket ball, which lacks the energy density of point-tipped Surface hardness interpolation (Kriging) ArcGIS (Arc- contemporary projectiles, such as the 7.62 × 39 mm bul- Map 10.4) was used to map the most likely distribution of lets commonly used in AK-47 and other assault rifles, Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 5 of 16 Fig. 4 Kriging inferred distribution of surface hardness variation and bullet impacts plotted for block 3 a block 5 b and block 6 c. d Values for block 6 have been plotted on a limited scale (243‑330) to highlight variation in values associate with bullet impacts which may not be evident at a large scale as illustrated in Fig. 5. The matchlock muskets used in the Civil War only had an effective range of 183–380 m and swiftly lost velocity  having reached a maximum speed of 180 m/s . As Powick Church is in an elevated position it is likely that the Parliamentarian soldiers had to fire up slope, which would have further decreased the damage potential of the ballistics. Upon impact, the ballistic has noticeably removed some of the surface, and left the bullet imprints investi- Fig. 5 A simple illustration of energy density and dispersal in an gated here. Within this newly exposed surface the clay AK‑47 impact vs a Matchlock musket ball impact content within the sandstone matrix will have compacted and realigned itself with the impact, thus reducing per- meability and susceptibility of the material to deteriora- the Civil War and the ballistics used in this test, a.22 tion processes. While it was not possible to sample the calibre lead bullet is soft and deforms easily  reach- stone at this listed Grade I building, this principle has ing a maximum of 275–365 m/s, thus also falls into the been tested using similar sandstone . Thin section ‘low impact’ group of ballistics, penetrating relatively analysis showed that at the point of impact of a low-cal- little into the impacted surface . We hypothesise ibre bullet, the clay minerals in the cement matrix rea- that the relative strengthening of the surface within the ligned with the direction of impact (see Fig. 6). While impact areas observed on Powick Church is due to rea- there are differences between the ballistics used during lignment of the clay matrix within the sandstone surface, Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 6 of 16 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. Between 1644 and 1646 Oxford was under siege by the Parliamentarian troops, a response to the entrench- ment of the court of Charles I in the city and its new status as the de facto capital. This new status trans - formed city life as the infrastructure and population were strained by the pressures of the incoming troops and new demands of maintenance and supply-lines . Fig. 6 Realignment of clay matrix within sandstone upon impact of This situation changed when, on 24 June 1646, Royalist a ballistic troops withdrew from the city ahead of an occupying Parliamentarian force . With the arrival of the Par- liamentarians a new, iconoclastic stance took form on in a process comparable to that observed in the simula- the streets of Oxford, manifesting itself in an antagonis- tion tests of .22 calibre lead bullets on a similar sand- tic approach to the city’s places of worship. While the stone surface in previous research . Surprisingly, this destruction of religious icons has at times been exag- could indicate that a singular impact point from a low- gerated in historical discussion of the Parliamentar- impact projectile (such as a musket ball) could actually be ian armies, it was a real and meaningful phenomenon, stronger than the material surrounding it. part of a wider official drive against images . It is However, when ballistic impacts are closely spaced thought, for instance,  that the University Church together there does appear to be a more focussed dete- on the Oxford High Street, and in particular the portico rioration, as demonstrated in block 6 analysis (Fig. 4c, containing the statue of the Virgin Mary and Child, did d). As shown in Fig. 4d, which was plotted on a limited not escape this destructive ideology (see Fig. 7a–c). At Leeb hardness scale to reflect variations within the indi - the time the destruction took place the portico itself was vidual block, the areas immediately surrounding the large relatively new, built in 1637 by Nicholas Stone. It has impacts have deteriorated further (Leeb values ranging since been repaired in 1865 , which included infill from 243 to 290) than the areas towards the bottom of of the bullet impacts with lime mortar and reconstruc- the block (Leeb values ranging from 280 to 330). This tion of the nose, following initial repair in 1662 . As leads to the hypothesis that low-impact ballistic damage such, discussion of conservation efforts of this heritage in principle does not cause extensive weakening of the must incorporate the subsequent repair works within surface; in fact, a singular impact could exhibit strength- the historical context of this initial, ideology-driven act ening rather than weakening of the surface, though this is of destruction and its place in the historical narrative. measured through about 350 years of exposure, but that In the remainder of this section, the deliberate destruc- clusters of low-impact damage do lead to enhanced dete- tion of heritage during conflict will be discussed, as well rioration of structural strength of the block and therefore as the impact of repairs on accurate damage assessment. need to be assessed as a potential conservation risk. Methodology Case study 2: ideology‑driven damaging of St. Mary As in Case Study 1, surface hardness was used to deter- the Virgin, Oxford, UK mine relative deterioration of the surface. This was In this case study, deliberate damage to build heritage- quantified using the same Equotip 3 with D-type probe. representing ideology-driven “cultural terrorism” and Sampling was directed by the features of the statue, e.g. its resultant damage by the Parliamentarian troops out- chin, nose, crown, neck, etc. (Fig. 7e), and with notes lined at the beginning of “Case studies 1 and 2: civil war taken on sections where supposed ballistic impacts in Great Britain; ideology-driven and collateral dam- were located (Fig. 7d). Where an impact had taken age (1642–1651)”—is contrasted with the unintentional place the area directly adjacent to the repairs was meas- damage to heritage caught in crossfire illustrated in the ured, rather than on the infill of the indentation left by Case Study 1. This case study investigates the deliber - the ballistic, which would merely have measured the ate damage to St. Mary the Virgin on the High Street in strength of the lime mortar rather than the damage to Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 7 of 16 Fig. 7 a Overview photo of the statue. b Damage to head and neck of the statue. c, d Sites of suspected ballistic impacts. e Rock Surface Hardness (Leeb values) results, n = 10 per site stonework. The mean hardness value, presented in the value 240) shows noticeably lower Leeb values than the figures, was calculated using 10 repetitions of impact non-impacted side (left, Leeb value 280.8). This trend measurements at each sample site, following previously reverses on the chin and lower cheek, where impacted established procedure of using multiple measurements areas measured were higher on the impacted side than in one surface area to offset outliers [24, 40, 41]. the non-impacted side. However, when the variability of the measurements is taken into account as an indicative Results factor in weathering progress  with higher standard As shown in Fig. 7c, d, there is no obvious visual pat- deviations indicative of relatively more intense weath- tern of accelerated deterioration of the impact zones. ering of the surface, three distinct groups of measure- On the neck of the statue, the impacted side (right, Leeb ments emerge; as Fig. 8 shows, group 1 consists of high Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 8 of 16 variability measurements (standard deviation range 61 in surface strength can be contributed to the ballis- to 80) indicating a further developed weathering pat- tic impacts. However, experimental research is needed tern, and encompasses the more vulnerable sections such to conclusively quantify the influence of alien material as the crown and the intricate portico. These intricate introduction on impact site deterioration. features are particularly vulnerable to weathering pro- cesses because of their relatively high surface to volume Colonialism and cultural vandalism ratio, as noted by de’Gennaro et al. . Group 2 consists The erosion of cultural pride under a colonial regime as a of impacted areas, which are mainly located in the less country-wide phenomenon has been remarked upon by vulnerable sections of the statue such as the neck, with scholars such as Taruvinga and Ndoro , as indigenous smooth carved surface and a higher volume to surface sites and art often faced neglect if not outright vandalism ratio. Group 3 consist of similar features to Group 2, less- within colonial regimes. The disregard for indigenous cul - vulnerable areas, but without the presence of impacts. ture during periods of colonial rule as well as the deliberate The clustering of the impacted areas of Group 2 (mean destruction of culture to establish dominance are themes Leeb value 246.36), which are in sections of the statue that resonate in conflicts throughout history in what Bevan comparable to those in Group 3 (mean Leeb value considers “calculated acts of cultural annihilation” . In 260.75), indicates that an overall deterioration of sur- particular, in times of conflict site security and heritage- face structure where a matchlock musket ball has hit at protective legislation can be either ineffective or unen - this site led to a reduction in mean Leeb value of 5.52%. forced; this is illustrated by the case study presented here, The standard deviation does not vary noticeably between where boredom of troops superseded any awareness of the the two groups, respectively 51.06 (Group 2) and 51.71 cultural importance of the sites they targeted for sport. (Group 3), indicating that difference between the two The protection of indigenous culture in particular can be groups is based on a general lowering of the Leeb value at risk when an external force is in conflict with the local where impacts have taken place, rather than an increase population, increasing the risk of vandalism and neglect. in measurement variability. In this case study, we explore vandalism during the 19th Difficulties in accurately assessing the long-term con - century, when weaponry and ammunition had evolved sequences of these ballistic impacts is exacerbated by the from the matchlock muskets discussed in case studies 1 presence of the repairs carried out in 1865; the addition and 2 to the more sophisticated percussion lock rifle. of lime mortar to the cavities in limestone of the statue obscure the impact cavity and prevent measurements Case study 3: damage to San rock art, Giant’s Castle Main of the impact surface. Furthermore, later addition of Cave, Drakensberg South Africa alien material has been noted to accelerate deteriora- The Main Caves at Giant’s Castle in the uKhahlamba- tion in heritage structures (e.g. ), which needs to be Drakensberg Park of KwaZulu-Natal, forms part of an accounted for when assessing the relative impact of bal- UNESCO world heritage site . These panels were listics on surface deterioration. As this limestone statue painted starting approximately 3000 years ago, and were was repaired using lime mortar it is assumed here that subsequently enhanced and expanded over the centuries the elastic modulus and moisture retention behav- following, by the San who inhabited the interior of south- iour was compatible and that therefore the reduction ern Africa until approximately 1870 . During the Lan- galibalele uprising, British troops under the command of Captain Barter entered the area and took refuge in the Main Caves in autumn 1873 on their way to the projected battle site of Bushman’s River Pass (KZN Wildlife, pers comm. 04/04/2017), . This troops formed part of a larger campaign led by Major Durnford and was to cross the Giant’s Castle Pass to join with the other troops trav- elling through the Champagne Castle Pass under Captain Allison and troops from the east led by Major Durnford himself . Captain Barter’s troops took refuge for the night and built a shelter under the rock overhang (Fig. 9) Armed with, likely, percussion-lock muskets  the troops evidently decided to use the San Rock Art for tar- get practice (Fig. 10a). This blatant vandalism focussed Fig. 8 Plot of mean Leeb values and Standard Deviation per predominantly on, but not restricted to, the main panel measured site. N = 10 for each site (Fig. 10b), spanning a number of figures including two Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 9 of 16 Due to the sensitive physical and social nature of San Rock Art it was not possible to acquire measure- ments at this site. However, visual analysis shows that the soldiers were likely standing directly in front of the left hand side of the large panel, shooting directly at the large eland (Fig. 10d) where energy appears to have dis- sipated from a central point, as illustrated in Fig. 11a. In contrast, the therianthropes (Fig. 9c) appear to have been shot at from a more sideways angle (approxi- mately 135°), as evidenced by the elongated impact (Fig. 11b). Visual comparison indicates that bullets shot at this kind of angle tend to ‘gouge’ the rock face, leav- ing a deeper indentation than those bullets shot at a 90° Fig. 9 Shelter built by Captain Barter’s troops within the Main Cave. angle and potentially leaving the surface more vulner- The Rock Art is situated on the rock face to the right of the shelter able to deterioration. (not visible in this image) 20th Century conflict large and one small therianthropes (mythical being which A century after the incidents illustrated in Case Study 3, is part human, part animal) and hartebeests (African a civil war broke out in Spain (1936–1939) which saw the antelopes), as well as hunters carrying bows and arrows Republicans fight against the Nationalists led by Gen - (Dr Rachel King, pers comm 24/11/2017). eral Franco. This conflict included a besieging of Madrid, Fig. 10 a Overview of the site, b therianthropes (half‑human, half‑antelope), hartebeest and hunters with bullet damage, c close up of bullet damage shot at approximately 135° angle relative to rock face, d close up of bullet damage shot at approximately 90° angle relatively to rock face Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 10 of 16 inflicted very soon after the completion of the building. Therefore, ballistic damage was not superimposed to any previous weathering process and any differences in dete - rioration behaviour can therefore be attributed to bal- listic 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 weather- Fig. 11 a Bullet impact at 90° relative to the rock face, related to ing inheritance might alter the long-term response of the Fig. 10d. b Bullet impact at 135° relative to the rock face, related to stone to ballistic impacts [10, 52]. Fig. 10c Case study 4: Complutense University of Madrid The example of the Spanish Civil War once again affords a stronghold of the Republicans, for 2.5 years from July a challenging case for assessing the challenges of ballis- 1936 to March 1939. Regular skirmishes between troops tic impacts within cultural heritage conservation. Today, left their mark on the city. Examples of this include the the School of Medicine of the Complutense University ballistic impacts on the 18th century Alcalá Gate (see is designated as being for the “Good of Cultural Inter- Fig. 12) which superimpose on previous ballistic damage est” (which is the highest level of protection for cultural generated during the Peninsula War in the 19th century. heritage in Spain) by virtue of its central role in the War. The case study discussed here, the School of Medicine The site itself has a long history. In 1836, the 15th cen - of the Complutense University of Madrid, represents not tury Alcalá University was moved to Madrid. A new only this 20th century damage and its associated increase campus in the northwest area of Madrid was planned in ballistic impact power, but also provides a very good in the late 1920s and Miguel de los Santos Nicolás was baseline for impact measurements; this war damage was Fig. 12 a Impacts on decorative pillars of the Alcalá Gate and b ballistic damage to corners of arch Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 11 of 16 Madrid during the 19th and 20th century. Almorquí stone is a granular porous (~ 20% porosity) biomicrite with up to 10% of terrigenous components (mainly quartz and clay minerals) as measured in an earlier study by Fort et al. . This area was chosen, as granular biomicrite resembles in both appearance and properties to building sandstone found in previous cases studies. Recent conflicts tend to involve a wider variety of armament and ammunition, thereby increasing the vari- ability 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 Fig. 13 Overall view of an area of the building showing ballistic added on an impromptu basis to the arsenal of the fight - impacts ers) and shrapnel impacts from nearby bomb explosions. Shrapnel fragments include lead balls as well as steel frag- ments of different shapes and sizes. This contrasts with commissioned as the architect of several buildings in this the previous case studies in which all projectiles impact- new Campus, including the School of Medicine . The ing on stone came from the same source and were similar School of Medicine was built between 1930 and 1935 and in size. Therefore, a key issue at this site is the relation - the Spanish Civil War commenced shortly after the build- ship between impact size and resulting damage, which is ing was finished. The university campus was assaulted quantified here. between 15 and 18 November 1936 and was part of the battlefront throughout the rest of the war (1936–1939). Consequently, the building was severely damaged. Methodology Between 1941 and 1945 the damaged sections of the Three damaged window ledges were selected to char - building were repaired, or where necessary rebuilt, by acterize the mechanical properties of the areas affected Miguel de Los Santos, incorporating bullet and shrapnel by impacts. Ultrasound Pulse Velocity (UPV) was meas- impacts across the whole building façades (see Fig. 13). ured with a CNS electronics Pundit portable ultrasonic The building is made mainly of brick, with the plinth, test equipment, which can detect a reduction in stone window ledges and other decorations made of limestone. strength even when no deterioration is visible at surface In this case study, we focussed on the window ledges level . While UPV investigations were attempted at (Fig. 14), which are built out of “Almorqui” stone from case studies 1 and 2, it was not possible to obtain meas- Alicante, east Spain, which was a popular stone type in urements on those sites due to interference by metal reinforcement structures within the stonework, such as pinning, which interfered with the signal. It was, how- ever, 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 dam- aged ledges 30 measurements were taken on an undam- aged 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 ellip- soid 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. Meas - Fig. 14 Impacts of different sizes in a window ledge. Smaller ones, urements were taken in a 100 × 20 cm area, so different which are likely the result of small size shrapnel, show inside granular sizes of impacts were measured. Measurements were disaggregation, while larger ones, coming likely from either rifles or large steel shrapnel, flaking, scaling and loss of fragments taken using a grid with a spacing of 6 cm (horizontal) Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 12 of 16 and 3 cm (vertical). UPV was measured in each point of As it is likely that these impacts have deteriorated sub- the grid with 1 MHz transducers, plasticine as contact surface structural stability, rather than just surface and medium, and a constant spacing between transducers near-surface deterioration as measured by the Equotip of 3 cm. Leeb hardness was measured as the average of Leeb values, additional Ultrasound Pulse Velocity (UPV) three impacts for each point of the grid. were taken which detect voids and fissures. As Fig. 16 illustrates, there is a visible logarithmic correlation Results between the impact area and UPV, which fits well with Leeb values, representing surface hardness, have been the visual examination of impacts: the smallest ones show plotted against impact size (Fig. 15) using undamaged some dusting or granular disaggregation within, and as stone as the benchmark (0). At first sight, there is no clear the grow larger, material loss scale also increase, going correlation between Leeb value and impact size, although from granular disaggregation, through flaking, to eventu - smaller impacts (less than 6 cm ) show more variable ally show losses in small chunks related to fracture forma- behaviour than larger ones. The total average values for all tion through energy dissipation. Where impacts had taken the impacts displayed a high standard deviation showing place close to the top surface of the ledge, thereby lacking that there was no common behaviour for all the impacts. confining pressure from the top, fracture development This is likely caused by the above-mentioned coexistence was more obvious which is also reflected in lower values of rifle and shrapnel impacts, as well as the possibility of than expected according to the logarithmic trend line. short-range impacts of small projectiles causing a similar To further this potential relationship between subsurface size impact to long-range larger projectiles. deterioration and impact size and placement, the results In smaller impacts the surface exhibits similar compac- were mapped using ArcGIS and 3D scanning (Fig. 17).The tion patterns to those observed in the older, lower force results show large horizontal and perpendicular to the sur- impacts demonstrated in Case Studies 1 and 2, strength- face factures, which are the main “bulk” changes in these ening the assumption that smaller impacts are caused by ledges. These window ledges are confined laterally but lead shrapnel similar to musket ammunition. Therefore, unconfined vertically on the top, and that affects the frac - this case study illustrates the differences shown in Fig. 5 turing pattern of the whole ledge. Most fractures are hori- (Case Study 1) between energy density and dispersal of zontal and located on the top third of the ledge, regardless rifle impacts in which damage penetrates deeper in the of the size and position of impacts, which likely is related stone, and “low impact” lead bullets in which the majority to the lack of confinement of the ledges on the top face. of the damage associated with the impact is released on Larger shots also have a fracturing pattern which includes the surface. This stress release at surface level is likely to fractures parallel to the external surface. These are often exploit pre-existing weaknesses, such as bedding planes, concealed, but are here detected with UPV. to dissipate outwards. This follows the principles shown Unlike the results reported in case studies 1 and 2, by Barauskas and Abraitiene  who mapped surface where damage appeared to be restricted to the surface deformation around the impact site in multilayer fabrics. 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 struc- tural damage through fracture network development, Fig. 15 Leeb value (surface hardness) plotted against sample size Fig. 16 UPV measurements plotted against impact size Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 13 of 16 Fig. 17 Measurement maps of ledge showing the distribution of UPV and Leeb values in relation to visible impacts indicates the changing nature of the deterioration threat we need to fundamentally change the way we approach to heritage that more recent ballistic impacts pose. These conservation of ballistic impacts to reflect the energy and fracture networks can not only deteriorate the strength of penetrative nature of contemporary bullet impacts. the stone at time of impact but can also be exploited by weathering processes for more rapid deterioration of the Discussion stone on the medium- and long-term. While historic low- These case studies illustrate a temporal range of impacts, energy impacts, such as those illustrated in case studies namely the 17th, 19th and 20th centuries, which repre- 1 and 2, can exhibit very little long-term deterioration sent the ongoing development of ballistic weaponry. In of the wider stone block and give little cause for concern Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 14 of 16 particular, the contrast between the rounded musket consideration in conservation strategies, in terms of balls (Case Studies 1 and 2) and the more modern weap- the relative strength of the impact (Case Studies 1 onry of the 20th century highlights the increasing inten- through 4), the clustering of impacts (Case Studies 1 sity of the ballistic impacts. In addition to this, modern and 4), and the angle of impact (Case Study 3). warfare is characterised by a more extensive mixture of 2. The enhanced threat to built cultural heritage in con - coexisting weaponry. Where previously some damage or temporary conflicts lies in the increasingly-destruc - even compaction of the surface is associated with musket tive penetrative of nature of ballistics. While Case ball impacts, Case Study 4 has revealed the resonating Study 1 showed relative strengthening of the surface impact further into the stone, creating far more com- in singular impact sites (but not in clustered impact plicated fracture networks and energy dissipation than sites), the far more destructive artillery of Case might be visible on the surface. This increasingly pen - Study 4 showed a much more noticeable deteriora- etrating nature of ballistic missiles, both in terms of the tion throughout the stonework. This increasing sub - bullets themselves and the weaponry used to shoot them, surface damage beyond the immediate impact zone is a cause for grave concern for the future conservation needs to be taken into account when assessing dam- of damaged heritage in conflict areas; if ballistics con - age to both historic and contemporary sites. In addi- tinue to increase in strength both in terms of energy and tion, these measurements can be seen as a warning energy density at point of impact as well as increasingly of the continuing development of weaponry and the efficient penetration of a material, it will be increasingly effect that ballistics will have on heritage stonework difficult to stabilise heritage post-conflict. in future conflicts. The issue is further complicated by the increasingly high profile of cultural destruction as an act of estab - In this light, it is therefore important that the sci- lishing geographical and cultural dominance, as seen entific community continues to explore the impact of in recent conflicts led by Daesh/So-Called IS. As illus - ballistics on stone surfaces, building on the work pre- trated and quantified in this article, the targeted, as sented here to quantify the impact of conflict on stone - well as incidental destruction, has become more effec - work strength and deterioration. While it might seem tive and widespread with the integration of artillery obvious that older impacts from lower-strength artil- ingrained into tactics and army provisions many cen- lery create less damage, this research has identified the turies ago and has increased in destruction potential complexities associated with multiple impacts and has at pace with weapon development. While the impacts also provided the first quantification of ballistic impacts described in Case Studies 1 and 2 could be considered on historic stonework. a relatively harmless potential deterioration enhance- ment, Case Study 4 illustrates that, 70 years ago, guns Conclusions were already capable of creating substantial sub-surface As illustrated by the case studies, the impact of bal- destabilisation of stonework. This begs the question: listics on build heritage is of increasing concern; the what damage can weaponry now inflict? While little is development of artillery since the 1600 s shows the known of the material deterioration of heritage sites increasingly destructive trajectory of ballistics devel- subjected to contemporary ballistic impacts, Mol et al. opment. To fully understand the threat that historic  reported that even smaller impacts could now cre- as well as contemporary ballistic impacts pose to build ate substantial subsurface deformation. The in situ data heritage we therefore need to take into account when presented in Case Study 4 builds on the results pre- the conflict took place, e.g. how variable and penetra - sented in the experimental study , and underlines tive the ballistics were at the time, and use this knowl- the shift from the superficial damage created by musket edge to extrapolate the likely presence of subsurface balls (case studies 1 and 2) and percussion-lock mus- deterioration of the stone which is not visible from kets (Case Study 3) to far more destructive artillery in the surface. This study presents the first quantification recent conflict. There are therefore two lessons that of the impact of ballistics on historic stonework and need to be drawn from the case studies laid out in this shows the accelerating damage curve associated with study: the development of artillery over the centuries. 1. Targeted and incidental (cross-fire) destruction of Abbreviations culture is not a new phenomenon, in fact ballistic 3D: three dimensional; RSH: rock surface hardness; GIS: geographical informa‑ scars can be found on multiple continents ranging tion system—ArcGIS indicates commercial software system; KZN: KwaZulu‑ Natal; UPV: ultrasound pulse velocity. many conflicts and spanning centuries, as illustrated by our case studies. These impacts require careful Mol and Gomez‑Heras Herit Sci (2018) 6:35 Page 15 of 16 Authors’ contributions 9. Smith C, Burke H, de Leiuen C, Jackson G. The Islamic State’s symbolic LM collected the data for case studies 1, 2 and 3 and wrote the manuscript. war: Da’esh’s socially mediated terrorism as a threat to cultural heritage. J MG‑H collected the data for case study 4 and contributed to the manuscript. Soc Archaeol. 2016;16(2):164–88. Both authors read and approved the final manuscript. 10. Mol L, Gomez‑Heras M, Brassey C, Green O, Blenkinsop T. The benefit of a tough skin; bullet holes, weathering and the preservation of heritage. R Author details Soc Open Sci. 2017;4:160271. Department of Geography and Environmental Management, University 11. Frangipane A. From spolia to recycling: the reuse of traditional construc‑ of the West of England, Frenchay Campus, Coldharbour Lane, Bristol BS16 1QY, tion materials in built heritage and its role in sustainability today: a UK. Department of Geology and Geochemistry, Universidad Autonoma de review. In: Prykril, et al., editors. Sustainable Use of Traditional Geomateri‑ Madrid, Madrid, Spain. Instituto de Geociencias (CSIC, UCM), Madrid, Spain. als in Construction Practice. 416th ed. London: Geological Society; 2016. p. 23–33. Acknowledgements 12. Walter J. Popular iconoclasm and the politics of the parish in eastern The authors are very grateful for the goodwill of Prof John Lewin and the Pow‑ England. 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