Valuing the subterranean: The tunnels of Gibraltar in war and in peace

Abstract

This article argues that value can be a key concept for bridging between geopolitics and economic geography, providing a historicised account of a subterranean geopolitical space as it shifts from a valuation regime focused on strategic use value to one focused on commercial exchange value. This argument is pursued through an empirical investigation of the tunnel system within the Rock of Gibraltar, tracing how they have been valued differently in different times due to technological and geopolitical change. Empirically, the article traces the creation of the tunnels by the British military from the 18th century until the mid-late 20th century, paying careful attention to the role of materiality, geology, and the broader techno-political assemblages that enabled and sustained that investment (until they no longer did). Crucially, the empirical investigation continues into the present, as the geopolitical value of the tunnels has largely been replaced by efforts to extract commercial value from them. While most of the tunnels have not found commercial use, the paper finds that the most successful commercial enterprises have used them in ways congruent with their fortress origins and the materiality of the Rock. The article concludes by arguing that the value of subterranea is imagined at the point of initial human investment, but once that investment materialises the value emerges from a wider relational space – drawing together the geology of the site, the people who work there, and broader circuits of empire and capital.

Valuing subterranean geopolitics

The hulking, rusty gas turbines haunt the cavernous space of Calpe Hole (Figure 1), highlighting the ambitions – and challenges – of using subterranean spaces inside the Rock of Gibraltar. Activated in 1955 after a WW2 ration store (itself recently built during the war) was enlarged to house them, the generators powered Ministry of Defence (MoD) facilities throughout Gibraltar, and eventually fed into the civilian power network as well. Housing a power station inside a mountain required adaption: ‘Earthing the generators proved difficult due to the resistivity of the rock itself (p = 10⁶ mΩ/in. cube). Consequently, the main station earth was obtained by means of a cable down to sea level’ (Ministry for Heritage 2025, n.p.). Additionally, the constantly dripping water and high humidity inside the Rock required equipment rated for ‘outdoor’ use. After it was decommissioned in 1974 due to improved facilities outside the Rock, this humidity led to the site’s rapid decomposition. This brief story hints at the potential value of subterranea to a geopolitically-resonant and space-strapped polity such as Gibraltar, as well as the challenges of subterranean materiality to those endeavours.

Figure 1.

The Calpe Hole generating station. Photo by Katharine Hall.

This article focuses on the concept of value and its application to an in-depth consideration of the tunnels within the Rock of Gibraltar (Figure 2). Drawing inspiration from Perez and Herrera's (2020) work on critical approaches to value underground, I trace the emergence of value through a set of specific intra-actions between the tunnels and the geopolitical and geoeconomic context both of Gibraltar and the wider socio-technical assemblages of empire. I attempt to historicise the value of the tunnels, taking from Childs (2020) a concern with temporality, and the way subterranean spaces are produced for contemporary concerns and speculative futures, but then are folded into the present in sometimes unexpected ways.

Figure 2.

This map shows the three-dimensional nature of the tunnel system, as it was in 2003. Author's photo.

In the next part of the paper, I sketch out my theoretical lens for interpreting this case study. Specifically, I argue for value as a bridging concept between economic and political geography. I first trace the literature on materiality, territory, and terrain to frame my subterranean geopolitics as one that both includes the human body and its experience and moves beyond that to enfold a range of more-than-human forces, from the scale of the local to the imperial. I then outline my concept of value, which similarly sees value as contextually emergent from more-than-human assemblages, or valuation regimes, that turn nature into resources (Castree 2003). Whether the tunnels generate geopolitical value or geoeconomic value depends both on their specific materiality and on the wider imperial or economic assemblages in which they were enmeshed.

Inspired by Yusoff (2018, 3) I argue that the tunnels both emerge from, and are understandable in terms of, wider assemblages of empire that have little to do with ‘the subterranean’, such as weapons systems, data infrastructure, and even the chemistry of wine: ‘Geology is a mode of accumulation, on the one hand, and of dispossession, on the other, depending on which side of the geologic color line you end up on.’ The story of Gibraltar is one of (Spanish) dispossession and then of geological destratification in the service of (British) empire; the subsequent shift of the tunnels into a commercial value system – with the promise of capital accumulation – has had uneven success because of the materialities of the Rock itself.

In the first empirical section, I engage with the tunnels at their most valued, as part of the geopolitical infrastructure that rendered Gibraltar the ‘first outpost of Empire’ (Howes 1946). In the final empirical section, I counterpoint the boosterism of the first empirical section with a more pragmatic account of the minimal use value afforded in actuality to the British military and their successors in HM Government of Gibraltar from the extensive tunnel works. Intra-actions between the human and the geological, the political and the economic, and the aboveground and the underground are productive of different forms of value over time. I conclude the article by arguing for more historicised accounts of the various regimes through which value emerges, and which look to the intra-actions of subterranean spaces and the humans inhabiting them, while still seeing those intra-actions in relation to broader assemblages of empire and capital.

Deep thoughts

Vertical geopolitics, territory, and terrain

The idea of a ‘vertical geopolitics’ has, for nearly twenty years, been a staple of interdisciplinary thought. Within political geography, however, early debate centred on a Foucault-inflected literature of drones, surveillance, and power (Graham 2006; Gregory 2006; Kindervater 2016; Williams 2011). However, this changed with Elden's (2013) intervention, which drew heavily from Weizman’s (2007) interrogation of the use of the vertical dimension in the Israeli occupation of Palestine launched a reconsideration of the role of the state in producing vertically striated spaces (see Billé 2020). Adey (2013, 52) in his rejoinder to Elden asks, by way of contrast to this approach, ‘are there other ways of thinking volumes that are more open, more plural imaginaries that might not only describe other alternative volumes to inhabit?’ This more atmospheric approach to volumes centres on the sensing body rather than the (disembodied) governmental power (see also Campbell 2019). More recently, Jackman et al. (2020) have called attention to whose experiences of territory and terrain are ensconced in ‘mainstream’ understandings of those concepts: ‘to the extent that territory and terrain are conceptually linked to geometry and calculation, their histories need to be told, at least in part, in relation to histories of systems and cultures of scientific domination.’ Extending that point, Carroll (2015) describes how ‘uncolonizable’ spaces were rendered sensible to British audiences through literature. Perhaps more saliently, Hawkins (2020) attends to the aesthetic experience of subterranea, and how it was made sensible.

In many ways, this divide between calculation and experience continues to structure the literature on political geographies of the subterranean – the underground is seen alternately as a space in which state power is materialised or as a place in which the materiality of the underground simultaneously enables and constrains – that is, it affects – human agency (Clark 2017; Klinke 2021; Slesinger 2020). Gordillo (2018, 54) drew on this latter tradition in his assessment of terrain as a key concept for understanding the relationship between power and environment: ‘The starting point of a theory of terrain is therefore that the latter has physical dimensions that exceed its contingent territorial, cultural, and sensorial appropriations by human actors.’ That is, terrain cannot be reduced to what people do on and in it. Rather, the affective geometry of bodies, environments, and technologies must be examined in their specificity to understand their relations. This is a crucial intervention, coming as it does at a time when scholars have been rethinking territory using Deleuzo-Guattarian philosophy (Painter 2010; Usher 2020).

This rethinking has emphasised the material dimensions of territory over the more legal, calculative orientation of previous theorisations. As Usher (2020, 1032) argues, ‘territory as a material reality remains strangely ancillary and elusive, conceived as secondary to law, capitalism, strategy and networks.’ This anthropocentric conception of territory is contested by the politics of the current moment, in which capitalism, climate systems, and political movements are understood to resonate with one another in increasingly dangerous ways (Connolly 2019; Dittmer et al., 2011). Territory here must be imagined as more-than-human, composed of a range of human and non-human forces arrayed against and with one another in ways that are not reducible to state power. Usher (2020, 1034), citing Deleuze and Parnet (2002, 482-484) and hinting at this paper’s concerns, writes that ‘Territory as a rhizomatic landscape is akin to “Swiss cheese”, “with its gaps, detours, subterranean passages, stems, openings, traits, holes, etc.”, containing myriad possibilities for evasion from state oversight.’ It would be limiting, although not necessarily wrong, to take this claim literally. Indeed, Ballestero (2018) notes the sponge-like nature of the earth, highlighting the liquid flows, suction, and seepage that mark its depths. In the next section, I review the way value has been discussed in both geopolitics and in economic geography, with the aim of using the concept to highlight how the sponge-like tunnels of Gibraltar have been valued differently over time.

Value, strata and the subterranean

The multidimensionality of value (e.g., use value, strategic value, exchange value) makes it a useful concept through which to understand the intra-actions that occur with stratification/destratification (Perez and Herrera 2020). As indicated by those examples of value, the concept provides a useful bridge between economic geography and geopolitics, in that both sub-disciplines are interested in the production, capture, circulation, and retention of value and the sites associated with it. Whereas this may be obvious for economic geography, it might not be so for geopolitics.

Classical geopolitical writers rarely utilised the concept of value explicitly. Nevertheless, there is a tacit (buried?) conceptualisation of value. For instance, Ratzel’s idea of Lebensraum valued land for its life-sustaining and agricultural capabilities (Ratzel 2018 [1901]). That is, there was a use value to possessing territory, in that it would sustain a larger population and maintain an upward spiral of geopolitical power. Haushofer’s Geopolitik was more attuned to the industrial age, and valued territories for their ability to contribute energy or other resources necessary for autarchy (Herwig 1999). Similarly, Mahan (1890) and Mackinder (1919) clearly saw strategic value in particular spaces and territories, particularly as they enabled, or were threatening to, the use of maritime power. Here we can see the association of different valuation regimes with geopolitical space, allowing use and strategic value to emerge. Indeed, sometimes exchange value comes to the fore, putting a price on the use value of certain territories (as has recently happened with Diego Garcia – HM Government 2025). Broadly speaking, critical geopolitics can be understood as the study of the discursive work that went into these valuation regimes, legitimating investment (of blood and treasure) in state projects of colonialism and conquest. In this article I am specifically investigating the investment in, and valuation of, the subterranean across both the geopolitical (use value, strategic value) and geoeconomic (exchange value) registers. To do so requires looking at how various valuation regimes work.

Lee (2006) argues that there are three iterations of (economic) value that function in different ways but must be thought together. First, there is ‘value’, which focuses on the things, ideas, and services that are life-sustaining or critical to social reproduction. ‘Theories of value’, by contrast, refers to the abstract thought about value that can either ‘be validated in social practice or imposed in political practice’ (2006, 415). Finally, Lee outlines ‘values’, which are the things, practices, and ways of being that are deemed too important to be in the realm of economy (see also Perez and Herrera 2020). To bring these together, value can be understood as emergent from everyday assemblages; as Lee (2006, 413) argues:

The nature and relations of value emerge from the practices of economic geographies shaped and framed by diverse social relations and values which, in turn, reflect the material circumstances of social life as well as theoretical understandings and performances of Theories of Value.

That is, economic value is both rooted in various material dimensions of a given context (e.g., scarcity, abundance) as well as wider infrastructures (such as technological shifts in production) and dominant ideas of ‘the economy’ and how it functions. There is no clear distinction between the inside and outside, and consequently value always emerges in a specific relational context: ‘[E]conomic geographies are always becoming, always a product of interior and exterior influences, always fragile and always perpetually interrupted and reconfigured’ (Lee 2006, 418).

To think of value as a bridging concept between economic and political geography, it helps to think of value as inclusive of, but crucially more-than, the forms of value associated with capitalism (Henderson 2013). Indeed, it would be a mistake to posit a clear opposition between geoeconomic and geopolitical value (Cowen and Smith 2009). Rather, it might be observed that these types of value can be linked through specific territories and terrains, as they become subject to discourse and are assessed according to different (geoeconomic or geopolitical) theories of value.

For example, Bridge (2009, 1219) argues that resources are ‘a cultural category into which societies place those components of the non-human world that are considered to be useful or valuable in some way.’ These resources – whether oil fields or maritime chokepoints – require investment in order to stratify or destratify ‘nature’ to extract maximum value: ‘The creation of value is always linked with material transformations and the creation of new materialities,’ (Kay and Kenney-Lazar 2017, 301). Clark (2017, 213) echoes many when he argues that

Deleuze and Guattari keep coming back to the idea that our planet pulses with the possibility of destratification, new combinational possibilities, reorganisation. In this regard – all life in general – plays upon the potentiality of the stratifying-destratifying earth.

That is, life itself (and other, narrower assemblages) is produced by the intra-actions of different strata (Barad 2007), and the temporalities associated with them. This is most obvious in terms of fossil fuels and other carbon-based strata, which are harnessed by humans to boost themselves to more-energetic levels of activity. For this reason, the subterranean has long been of interest to colonial and state power (Braun 2000; Marston 2019; Mitchell 2011; Yusoff 2018).

As Perez and Herrera (2020, 585) note, state-centric valuations of certain subterranean territories or landscapes as strategic or useful must coexist with other valuation regimes. This is evident in, for instance, the competing valuation of the Cuban karst cave landscape by the state and by Cuban speleologists (Perez 2021). As complicated as questions of valuation regime can be, a further layer of complexity is added by questions of ownership. In short, ownership shapes the application of valuation regimes, even if it does not resolve those conflicts entirely. Melo Zurita’s (2019) analysis of sinkhole tourism in the Yucatan Peninsula highlights the tensions between commercial enterprise and state ownership of the sinkholes themselves in a way that resonates with the case study of this paper. This speaks directly to this case study, as the tunnels remain Crown property.

In the empirical case examined here, Gibraltar saw material transformation over several centuries, with its subterranean carved out painstakingly to maintain the fortress’s geopolitical value in the face of shifts in the wider techno-economic assemblages of empire. By the late Twentieth Century further de-stratification could no longer be justified as a direction for state investment; indeed as the British state dis-invested in Gibraltar the tunnels became subject to a new valuation regime, with the British Crown increasingly treating them as a commercial asset (Christophers 2010). Indeed, the latter part of this article documents efforts to locate the tunnels as a form of waste within a ‘minor history of value’ (Gidwani and Reddy 2011), abandoned spaces from which new value might be extracted in surprising ways.

Methods

As Squire and Dodds (2020) note, there is no singular way to approach studies of the subterranean. Following in the footsteps of Squire (2016a), whose research on Gibraltar inspired this work, I have endeavoured to approach the tunnels of Gibraltar through multiple methods. However, unlike Squire (2016a), I have followed the tunnels beyond the context of conflict with Spain to think about their relation to contemporary Gibraltar as a polity seeking to secure itself within the global economy.

This research is largely grounded in primary and secondary archival research. The UK National Archives at Kew hold records from the Ministry of War and the Colonial Office, both of which were central to the construction and governance of the tunnels, as well as the Foreign, Commonwealth, and Development Office (which has responsibility for relations with Gibraltar). The archives of the Royal Engineers Museum in Gillingham hold many technical reports on the tunnels as well as photographic records of the tunnelling. Collectively, these sources reveal the wide range of ways in which governmental and scientific knowledge was deployed in the production and maintenance of the tunnel network.

However, to understand the ways in which various strata (understood here both as geological formations and temporalities) are being brought into contact with one another to produce value (or not), it was important to trace the tunnel system into the present via interviews; in total five interviews were conducted with individuals who work for institutional users of the tunnels (Continent 8, the Gibraltar Wine Vault, AquaGib, Land Property Services [advisor to Government of Gibraltar]). The major exception was the Ministry of Defence (MoD), which declined to participate; however, one interviewee was formerly in the British military and was able to comment on the contemporary MoD use of the tunnels. Interviewees were asked about their institutional activities in the tunnels, the benefits and challenges of working in the tunnels, and how Gibraltar’s subterranean system was valued (or not) by the institutions in which they were situated.

The empirical findings are framed in a chronological way to highlight how the geopolitical assemblage of the Gibraltarian tunnels were initially highly valued for their politico-military capabilities, but now lack the same value because the wider geopolitical assemblage of empire has tipped into a new formation (Dittmer 2021). This fold within the paper reflects my intent to historicise the question of value and the subterranean, and highlight the importance of both the geology and the wider assemblage of empire. By showing the trajectory of Gibraltar’s tunnels through time, it becomes possible to show how multivalent and complicated the intra-actions between the earth and the aboveground assemblages of empire (and post-empire) can be.

Romancing the stone

Jutting south into the Strait connecting the Mediterranean with the Atlantic, the peninsula of Gibraltar is dominated by its eponymous Rock, largely composed of dolomitic limestone but flanked by twin strata of shale (Rose 2001, 2016). Its North Front rises to a height of 424 m, facing Spain with its most-famous profile. The main ridge of the Rock, however, extends to the south, with an equally sheer east face extending down into the sea. To the south and west the Rock is gentler, descending through a series of slopes and plateaus to end in low cliffs or, today, in areas that have been reclaimed from the sea. It is on these slopes and plateaus that the historical fortress and today’s city of Gibraltar have been located.

While the Rock features in clichés such as ‘as solid as the Rock of Gibraltar’ (Lambert 2005), it is notable that – being made of limestone – the Rock is actually quite permeable to water. While Squire (2016a) notes the role of the surrounding water on the elemental geopolitics of Gibraltar, I want to go further and highlight it within the Rock. Gibraltar’s ancient name, Mons Calpe, dates to the ancient Phoenicians, and refers to the ‘hollow mountain’. Indeed, before any tunnelling in Gibraltar, limestone dissolution caused by rainwater percolating through the Rock created a vast cave system that provided use value as shelter for the last known Neanderthals, clinging to the southern edge of Iberia during the last Ice Age (Finlayson et al., 2008). This fact provides a model for thinking about the Rock as simultaneously both a geological and hydrological phenomenon (Ballastero 2018; Peters and Steinberg 2019), useful for understanding the assemblage formed between the Rock and humans that emerged over time.

Most knowledge of the Rock’s geology was produced through the British military presence, imposed by force in 1704 and by treaty in 1713. The first geological map of Gibraltar was published in 1878 by the British Geological Survey to discover more potable water for the fortress (Rose 2016). However, the engagement of the British military in geological studies of the Rock dated back to the 1700s, because ‘The strength of the fortress [was] due to topographical features (influenced by their underlying geology) and their enhancement by military engineering’ (Rose 2001, 96). To maximise the use value of Gibraltar to the wider British Empire, geologic knowledge was crucial because British power quite literally rested on the Rock, using the mountain as natural elevation to provide strategic advantage. However, maintaining this use value over the next several centuries required further de-stratification, and would produce a deeper knowledge of the Rock. In the following section I document the capabilities that emerged during the Great Siege.

‘Works worthy of the Romans’

The tunnels within the Rock have their origins in the Great Siege of Gibraltar (1779-1783), in which the British fortress was cut off by the Spanish and French both by land and (mostly) by sea. The imposing Northern Defences of the Rock allowed the British to mount cannons well above their besiegers, who to reach the gates would have to cross the sandy isthmus connecting Gibraltar to the mainland, and then march down a narrow causeway with water on either side while cannonballs rained down on them (on chokepoints, see Dunn 2020). However, the Spanish and French forces managed to advance far enough south that they could hide ‘under’ the guns on the North Face and perhaps undermine the fortress with their own engineers. The first British tunnel was undertaken in 1782 to place a cannon on a stony outcrop, allowing the British to fire on these sappers. Therefore, destratifying the cliff face initially produced use value by enabling new angles for artillery fire: opening up geology to open up geometry. However, it soon turned into a tunnel system from which British artillery could fire from within the Rock itself, via portals opened in the mountain’s face, and through which soldiers could move between defensive positions (Goodwin 1927; Haycraft 1946). The method of tunnelling during the Great Siege was an entrepreneurial combination of early industrial mining techniques and battlefield improvisation using gunpowder and crow bars. Rather than imposing abstract form on the Rock, the miners followed fissures within the limestone when possible (Goodwin 1927). The tunnels in the Northern Defences were not finished by the end of the Great Siege but were completed afterwards.

When the siege ended, the Spanish commander was given a tour of the Northern Defences. The Duc de Crillon’s (reported) comment, that ‘These works are worthy of the Romans’ (Drinkwater 1786, 344), is noteworthy in two respects. First, it resonates with the Great Siege as an event that ‘made’ the reputation of Gibraltar as a site that is both key to, and emblematic of, the British Empire (Lambert 2005). That is, from this point on the survival of the garrison in Gibraltar during the Great Siege is seen as the basis for the ‘Second British Empire’, oriented through the Mediterranean after the loss of (most of) the North American colonies, and also as the archetype of the so-called ‘British Bulldog’ spirit. Second, the reference to the Romans – and British historians’ proclivity for reproducing this quote (e.g., Adkins and Adkins 2018; Connolly 1857; Gale 1969) – indicates how the Siege Tunnels are narrated as a lasting engineering feat of such value that they put the British Empire in the top tier of geopolitical powers throughout history.

‘The most dismal setting we occupied in the war’

While work on the Northern Defences continued after the Great Siege, it stopped between 1800 and 1895. Then there was a brief foray into new tunnels at the south end of Gibraltar, the beginning of today’s ‘southern system’. As with the Siege Tunnels’ use of existing fissures, this effort was shaped to work harmoniously with the caves that had given ancient Gibraltar the name Calpe (Gale 1969). For instance, a cave was lined with bricks to serve as a magazine, which was connected by rail to the docks. In contrast to this, and as a harbinger of what was to come, the Admiralty Tunnel was driven in an abstract straight line through the Rock to connect a land reclamation project within the port to the eastern (Mediterranean) side of the Rock, where stone was quarried (Figure 3). In the early 20^th Century, both the Admiralty and the City Council tunnelled in the Rock, using caves and tunnels within as water reservoirs and waterworks (Haycraft 1946). Fifteen reservoirs, each averaging 500,000 gallons of capacity, were readied for civilian and military use (Andrews 1958). By the outbreak of World War 2, there were four or five miles of tunnels within the Rock of Gibraltar.

Figure 3.

View down the Admiralty Tunnel, which was created to bring quarried stone from the east side of the Rock to the west's land reclamation project. Note the abstract straightness of the tunnel (the small light in the centre is in fact the other side of the Rock). Author's photo.

The renewed military emphasis on tunnelling in World War 2 came about because of changes to the nature of warfare since the Great Siege, which shifted the assemblage through which the fortress’s value was understood (Dittmer 2021). The development of long-range rifled artillery and air power radically changed the practicalities of a fortress. Rifled artillery meant that an enemy in the Spanish hills could destroy the walls of Gibraltar without ever even coming into sight, and air power meant that bombs could render the naval base unusable. ‘The bombs that fell on Gibraltar, and the power of the huge guns emplaced across the Bay with the one target in their sights, made it clear that there was no lasting protection in casemates and shelters’ (Andrews 1958, 195). Air attack could come from Italy or elsewhere, while the possibility of Fascist Spain joining the Axis meant that the German army might appear on the other side of the isthmus, where the Spanish and French had gathered 150 years earlier.

The problem was urgent and vital; space became even more valuable; stores, food, and equipment had to be built up, and protected; siege accommodation was required for the troops. It was obviously necessary to plan and develop a tunnelled system to meet these needs, and to give full protection from the then known types of air attacks, as well as from sea and land bombardments. (Gale 1969, 5; emphasis added)

The Rock was to be infrastructured as a fortress itself, allowing the garrison to withdraw into the protection of the mountain and stage a counterattack. The full panoply of military facilities outside the Rock had to be replicated within it: hospitals, generators, laundries, billets, command centres, etc. A further round of destratification was called for to reconstitute the past use value of Gibraltar.

The scale of the task was enormous, especially since at the time there were no miners in the British Army. The 180 Tunnelling Company of the Royal Engineers was formed in October 1940, after the fall of France made the vulnerability of Gibraltar apparent. A month later they were joined by a group of Canadian engineers, who brought with them techniques of petrol-based diamond drilling developed to aid in hard-rock contexts, which sped up the mining process. Other Tunnelling Companies joined in 1941, and the Canadians went home in 1942. The new methods of drilling and impetus for tunnelling resulted in a style of work that was significantly less harmonious with the geologic structure, with abstract, straight lines driven rapidly through the Rock (Rose 2019).

There were two major sites of work, one being the existing system in the Northern Defences and the other being the southern system. They were linked up in 1944, allowing someone to travel from the Northern Defences to the exit of the southern system without going above-ground. The term ‘tunnel’ does not do justice to some of the abstract volumes created; for instance, the laundry was 167 feet long and 40 feet wide, with 18-foot walls and an even higher arched roof (Gale 1969). By the end of the war, there were 24 miles of tunnels within the Rock. This was an imposition of human form in the Rock, attempting to retain value through destratification.

However, the intra-action between human bodies and the Rock was not an unmitigated success (Jackman et al., 2020). Contemporaries note that being immersed within the Rock was less than ideal (Squire 2016b). General Eisenhower described it as ‘the most dismal setting we occupied during the war’ (quoted in Andrews 1958, 199). The difficulty was in policing the boundaries of the mountain fortress. How was it possible to keep the bad things (moisture, bomb blasts, poison gas) out, while making it possible to easily bring necessities (lorries, people, fresh air) in? The mountain itself was permeable in ways that were both productive and dangerous to human life (see Melo Zurita 2020), and the military challenges then foreshadow some of the economic challenges of assembling value today, as I shall demonstrate.

Thomson (1946), in a report to the War Office, notes the more-than-wet ontology (Peters and Steinberg 2019) of the Rock in dramatic fashion:

The limestone formations in Gibraltar are so very porous that the water percolates through, and in some parts of the rock provides a constant rainstorm effect, which has very disastrous results on any form of iron roofing, such as Nissen huts.

Similarly, Haycraft (1946) notes moisture ruined the stockpiles of rations quickly, and that the dripping of water through the limestone caused everything inside to become damp and uncomfortable. General Eisenhower, who launched the invasion of North Africa from a command centre in the Admiralty Tunnel, linked the natures of the Rock and war itself into a singular affective experience of command:

Through the arched ceilings, came a constant drip, drip, drip of surface water that faithfully but drearily ticked off the seconds of the interminable, almost unendurable, wait which always occurs between the completion of a military plan and the moment action begins. (Quoted in Andrews 1958, 201)

In most tunnels concrete was used to level the floors, but the ceilings remained unlined, allowing stalactites to slowly extend towards the floor as water moved through the Rock (Rose 2019).

Paradoxically, there was also a desperate need to get water into the Rock. A classic problem of fortresses under siege is the provision of water. The city of Gibraltar’s water reservoirs within the Rock were linked up with the military reservoirs and military condenser plants via a system of water mains both inside the mountain or on the sheer eastern side of the Rock. Enough water was kept in the immense Calpe hollows to ensure the garrison could survive until the next rain (Haycraft 1946). This capacity was achieved in collaboration with the Rock, which ensured that no bacteria could access the reservoirs. Such non-human elements of the assemblage threatened the use value of the fortress under siege.

Another vital circulation within the Rock was that of air. Of course, having a whole garrison living inside a mountain, with generators and combustion engines working, posed challenges to the maintenance of life. Electric fans, aided by metal ducts that linked to the external atmosphere, worked to ensure that adequate fresh air was provided throughout the Rock. In practice, however, much of the energy circulating air through the Rock was provided by natural currents (such as the Levanter, a regular easterly wind) and differences in air pressure on different sides of the mountain. Of course, all these entrances had to be protected against the possibility of gas attack, so all external ventilators were fitted with gas filters, and all tunnels were capable of being sealed on short notice (Haycraft 1946). The importance of securing some flows, while keeping out others, dominated the rapid expansion of the tunnel system as the military sought to maintain the Rock’s use value as a fortress within the changing techno-military assemblage of empire.

The scale of the tunnel system, and the infrastructure that went inside the Rock – hospitals, generators, water mains, electrical systems, vehicle roads and parking – resonated with the existing ‘worthy of the Romans’ discourse of Gibraltar as a bulwark of the Empire and feat of British ingenuity. Nevertheless, the incredible amount of investment that went into building the tunnel system (which reached about 34 miles) was never actualised as use value; the threat to Gibraltar was over as soon as Italy was invaded in 1943. Still, a tremendous amount of money and labour was expended destratifying the Rock to produce a latent capability of the Gibraltar assemblage, rather than one actually activated in wartime conditions. The next section documents how that latent use value was maintained (or not) during the next transformation of the political-military-economic assemblage of empire.

Between a rock and a hard place

There was a respite in the tunnelling following V-E Day, and then post-war tunnelling resumed in 1956 and ended in 1968 (Rose et al., 2019). This last bout of tunnelling marked an effort to maintain the fortress’s use value as originally envisioned, but also to (again) reconstitute it for the age of atomic (and eventually nuclear) war that had emerged after World War 2.

‘Of such a design as to be dangerous in the event of a nuclear attack’

If the arrival of rifled artillery and air power had changed the calculus regarding Gibraltar’s use value as a fortress, then nuclear weapons heightened these concerns. The capacity of a single bomb or warhead to eliminate the naval base called into question the value of past investments; nevertheless, the Rock itself – and its extensive tunnel system – provided one of the few possibilities for a garrison to survive such an attack. This caused a renewed interest in the tunnel system.

A confidential report on the state of the tunnel system was produced by the Royal Engineers (Hughes 1964), examining the state of the tunnel system. The author notes a general state of deterioration and a lack of maintenance, but also notes some of the problems created from the rushed construction of the Second World War-era tunnel system. Not as many chambers had arched ceilings as ought to, and over time these ceilings were increasingly vulnerable to stress caused by further blasting or traffic vibrations. The event of the war had spurred a large investment in the Rock’s de-stratification, but the use value of this investment was altered by the explosive potential of the nuclear age.

The hurried construction of the World War 2 tunnels was, as noted before, not done in harmony with the geological structure. The report’s author notes that Great North Road (which connects the northern and southern systems) has a series of faults that transect it, and the lack of arched roofs means that ‘these chambers are of such a design as to be dangerous in the event of a nuclear attack’ (Hughes 1964, 11). Another tunnel that might be used as an escape route ought to ‘be used after a nuclear attack only in the event of an emergency’ (Hughes 1964, 12; one wonders what might constitute an emergency after a nuclear strike). The report notes that the geology of the Rock – in the context of a nuclear attack – lead to strategies for shoring up the tunnels used in traditional mining to be ‘worse than useless’. For instance, timber supports are vulnerable to the aforementioned dampness, ‘rotting continually, and the deterioration is not shown by collapse or bending under weight. Furthermore they are best suited to gradual loads only, and the shock loading that could result from a nuclear attack may not be withstood’ (this and previous, Hughes 1964, 20). While the report indicates remedial actions that could have been taken to improve the readiness of the tunnels to serve as protection in a nuclear attack, it was unclear that the strata that sheltered soldiers from air attack in the Second World War would provide use value in the atomic era.

Due to the cost of maintenance, the MoD has withdrawn from most of the tunnel system, maintaining roughly 15-20% of it. The role that Gibraltar served in World War 2 – as a command centre for the invasion of North Africa – was phased out with further technological change. The last ‘watch keeper’ in the Command Centre (ComCen) within the Rock explained:

INTERVIEWEE: During heightened alert state or military exercise, I would become watch keeper down inside the ComCen. That would entail working from what we call Current Ops, updating all the maps with what’s going on in the outside world. So you’ve got an action station a bit like Churchill’s War Room, if you like, for the modern day. It wasn’t frequent, maybe four to six times in four years.

AUTHOR: And why did they eliminate [that position]?

INTERVIEWEE: The cost of maintaining areas on the ground is phenomenal when you can achieve the same on a laptop with an Intel Pentium processor, you know, in the back office somewhere else at 1/10^th the cost. So the times have moved on. (UK military retiree interview, 19 May 2020)

According to this interviewee, the tunnel system is currently internationally valued for training purposes; indeed, the Gibraltar Regiment is seen as subject-area experts in OTAC warfare (Operations in Tunnels and Caves), and both British and allied troops come to practice within Gibraltar. Areas in the southern system also remain in MoD use as ammunition storage. In short, there remains some geopolitical use value in the tunnels.

‘Being inside the Rock has its own challenges’

But what about the roughly 80-85% of the tunnels that are no longer maintained by the MoD? How has their value been assessed as they have shifted from military rationales for investment to broader assemblages of value-making? When British sovereignty was exercised over Gibraltar in 1704, all of the land in the territory became Crown Land. Therefore, when the MoD no longer had use for tunnels, they could simply be transferred to HM Government of Gibraltar without being subject to market valuation, as the territory’s government is simply another manifestation of the Crown. Rather than selling the tunnels, therefore, ‘interest’ in specific spaces by different aspects of the Crown is simply re-assigned via a memorandum. Once re-allocated, the Gibraltar Government attempts to use the tunnels for the good of the people of Gibraltar. This is done via Land Property Services, a private firm of surveyors that works exclusively as advisors to the government (LPS interview, 6 May 2020). The use value generally takes the form of storage for government ministries, such as for medical supplies, and of course the reservoir system. Gibraltar actually has two water systems; one with fresh water for drinking and another with saltwater for non-potable uses such as toilets and firefighting. Both kinds of water are held in 12 reservoirs within the Rock, and the water mains are run through pedestrian tunnels originally made by the MoD (AquaGib interview, 15 May 2020). Clearly this is a different form of use value than originally imagined, but it is use value nonetheless.

Another potential use for subterranea is to be licensed for commercial use. In this way the tunnels remain in government ownership but become coded by exchange value rather than use value. One interviewee from Land Property Services (interview, 6 May 2020) argues that the problems of tunnel deterioration noted in the 1964 report have only continued, and potential commercial bidders must have both an economically viable use for the space and be willing to meet regulatory standards. Once the tunnels are moved from military to commercial use, they became subject to Health and Safety regulations from which the MoD is exempt. Therefore, any potential use of the subterranean requires enough profitability to withstand a substantial initial investment in shoring up the tunnels, making them suitable for employees to work in, and so on. Tenders for interest in developing the tunnels take two forms: the Government might put out a tender for a specific use of a space to benefit the community, or expressions of interest for potential uses might be solicited to get fresh ideas.

A general pattern can be seen. The most successful enterprises are successful to the extent that they are congruent with the fortress origins of the tunnel system. That is, the tunnel system was devised to enable some life-giving circulations while protecting life from the hostile outside. Beyond heritage tourism and a few underground car parks or storage units (both in high demand in space-strapped Gibraltar), there have been only two major commercial enterprises at work within the tunnels.

The first major enterprise is a data centre built in the Admiralty Tunnel. This tunnel was originally a transport link between the east and west sides of the Rock but gained in prestige as General Eisenhower’s headquarters for the invasion of North Africa. According to an interviewee from Continent 8, in the wake of the MoD closure of the command centre, the data centre was founded by Sapphire Networks, who valued both the mythology of the Rock and its geological properties to make it a site for data storage: ‘the Cloud in the Rock’. However

Our predecessor mistakenly thought that being in the Rock he would get free cooling, and that the Rock would absorb the heat and therefore use very few compressors to cool [the data centre]. Unfortunately, limestone is an insulator rather than a conductor of heat. So it works against what he was thinking. (Continent 8 interview, 24 April 2020)

Continent 8, whose main clients are in the online gaming sector, had signed a contract with Sapphire Networks to rent space in the data centre (Gibraltar was then emerging as a major centre of regulated online gaming in its efforts to re-make its economy after the MoD downscaled its presence). When Sapphire Networks withdrew, Continent 8 took over the data centre rather than disappoint their clients, and now have to live with the effects of their predecessor’s poor geological knowledge. However, Continent 8 does benefit from the Rock by both drawing on the discourse of the Rock’s fortress-like qualities in their marketing (Figure 4), and from the site’s excellent security; there are only two entrances to the tunnel and the geologic structure of the Rock provides protection from electronic surveillance (Continent 8 interview, 24 April 2020; see also Taylor 2023).

Figure 4.

An advertisement for Continent 8, drawing on the fortress discourse to sell data security. Author's photo.

However, Continent 8 had to run a huge bank of fans to push the immense heat produced by their servers into the secondary tunnel system (this practice has since stopped), as well as run dehumidifiers constantly to counteract the percolation of water through the limestone. ‘We’re here because it was available, not because we wanted to be inside the Rock. Being inside the Rock has its own challenges and engineering issues, as anyone can imagine’ (Continent 8 interview, 24 April 2020). The exchange value here is primarily discursive in nature, with the materiality a double-edged sword. The challenges of producing commercial value from the tunnels now mirror some of the challenges faced during World War 2 (excess moisture, air circulation).

The other major enterprise within the tunnels is the Gibraltar Vault, a storage site for fine wines. Like Continent 8, the Gibraltar Vault values the associations with the historic fortress and its inbuilt security:

The largest natural, underground wine storage facility in the world. Housed deep within the iconic Rock of Gibraltar. What else on Earth could stand so imposingly over your most precious investment? […] We believe your liquid assets deserve something special. A fortress. And that’s precisely what we are. (Gibraltar Vault 2024, n.p.)

However, unlike Continent 8, the Gibraltar Vault benefits from working with the tunnels’ materiality rather than against it.

It’s about temperature, stabilisation, and humidity. […] So actually, the tunnels are perfect[…] All it is, is a flat 14 to 16 [degrees Celsius] all the way through, so it is a constant temperature so that your wine can evolve over time. But [also] humidity, because most fine wine is under cork. That allows some of that moisture to be retained in the cork, so it doesn’t dry out, but not too much that it doesn’t damage the labels, etc. And also the lack of light, because light will actually destroy a part of the colour and tannins in the wine. A dank and dark cave is lovely. (Gibraltar Vault interview, 19 May 2020)

Of particular interest to the Gibraltar Vault is the Levanter wind (mentioned above), which provides natural regulation of the tunnels’ microclimate; when humidity rises too high the staff open or close particular doors and the humidity evens out (Gibraltar Vault interview, 19 May 2020). This level of microclimate regulation is produced in competitors’ vaults via expensive climate control systems; in effect the Gibraltar Vault resonates with the materiality of the Rock rather than contrary to it, as Continent 8 does. Nevertheless, both enterprises benefit from the historical associations of the Rock with security.

Dead ends

The aims of this paper have been to (1) argue for value as a concept that bridges between geopolitics and economic geography, (2) historicise the subterranean by tracking value over time, and (3) highlight the importance of wider assemblages (in this case, of empire) to the political geology of subterranea. The overarching story with which I have tried to accomplish these aims, it might be argued, is one of tremendous imperial investment, most of which has failed to be valued for either use or exchange in postimperial times. We might think of the tunnelling as destratification that generated geopolitical use value; however as other elements of the wider politico-economic assemblage have changed (the rise of nuclear weapons; the digitalisation of military command-and-control; the emergence of a post-colonial Gibraltar, both politically and economically) the raison d'être of this massive investment has been lost.

Further, excluding the (admittedly not insignificant) parts of the tunnel system still in use for tourism or state purposes, only 3 km out of the 55 km network has produced commercial value (1 km is in use by Continent 8 and a further 2 km by the Gibraltar Vaults). Of course, part of the political potential of bridging across strata is the possibility of the dead being brought back to new purpose; as one interviewee pointed out (6 May 2020), it would have been impossible twenty years ago to foresee the potential of a data centre in the Admiralty Tunnel. Perhaps the next use of the tunnels is just around the corner, temporarily out of sight.

However, the barriers to entry are quite high given the speed with which the tunnels were built, and their materiality poses specific challenges. The tunnels themselves are interconnected, and not prone to the segmentation that capitalist property regimes prioritise. This can be politically positive – the interviewee from Land Property Services cites the tunnel topology as contributing to cooperative relations between the MoD and HM Government of Gibraltar (see also Woon and Zhang 2021). But nevertheless one can see how the topological nature of the tunnel spaces limits the commercial value for the unclaimed 52 km. Proximity to the ‘outside’ is generally advantageous as that is where the customers are; this makes only a small sub-set of the tunnels interesting to bidders, and to get to tunnel spaces further ‘in’ could mean going through other users’ spaces. The more the first-choice tunnels are occupied, the less accessible the remainder are; there is no public ‘street’ that connects these spaces, rather the spaces are the street.

To conclude, looking at the tunnels in terms of use or exchange value allows for an analysis that historicises investment in destratification with different valuation regimes associated with imperial and postimperial dispossession and accumulation (Garrett et al. 2020; Yusoff 2018). The intra-actions between the Rock and the people at work within it shaped both and produced their agencies; nevertheless these agencies were also shaped by broader imperial techno-political assemblages. When these activities were congruent with the geologic structure of the Rock, they produced stable interventions; when they were hurried and abstract in form their interventions have proven less long-lasting in value. The use value of subterranea is imagined at the point of initial human investment, but once that investment materialises the value emerges from a wider relational space – drawing together the geology of the site, the people who work there, and broader circuits of empire and capital.