Introduction
The failed military coup of 18 July 1936 triggered a bloody civil war in Spain, lasting until 1939 and culminating in the establishment of a military dictatorship. This conflict divided Spanish society and reshaped the landscape through the creation of extensive wartime infrastructure, including trenches, machine-gun positions, airfields, and shelters. Among the most significant of these was the Bilbao Defensive Belt—later renamed the Iron Belt—constructed by the Basque Government to defend the city and its industrial base. However, like the Maginot Line and other similar defensive works in inter-war Europe, it proved militarily ineffective: it was breached by Francoist forces in just two days in June 1937 (González Ruibal, Reference González Ruibal2020a: 110). This contrasts with the image of invincibility that surrounded the Iron Belt from its conception, and which has endured to the present day.
Far from debunking this myth following its conquest, Franco’s regime actively cultivated the image of invincibility, using imagery, such as Carlos Sáenz de Tejada’s idealized depictions of victorious soldiers, to aggrandize the triumph. This narrative persisted throughout the dictatorship (Líbano Silvente et al., Reference Líbano Silvente, Salazar Cañarte, Vega López, Baizan, Zuazo Gibelondo and Olabarrieta2021: 124) but has been reinterpreted in the democratic era (1975 onwards). Today, the Iron Belt is often framed as a symbol of Basque resistance (Herrero Acosta & Ayán Vila, Reference Herrero Acosta, Ayán Vila and Urtizberea2016: 109–15), with Basque nationalist governments promoting the figure of the gudari (Basque soldier) and reconfiguring the Francoist narrative to emphasize the idea of heroic defence (Martínez Rueda, Reference Martínez Rueda2022). An example of this narrative shift is the absence of public debate surrounding the restoration of the name Bilbao’s Defensive Belt replacing the Francoist terminology Iron Belt (González-Cantera & Rubio-Campillo, Reference González-Cantera and Rubio-Campilloin press).
Archaeology offers a critical means of challenging such established narratives (Moshenska, Reference Moshenska2010; González Ruibal, Reference González Ruibal2020a). Since the early 2000s, archaeological research has been conducted on wartime structures. The Iron Belt is notable for having many of its elements superimposed on sites associated with the three nineteenth-century Carlist Wars, opposing reactionaries to liberal revolutionaries (Martín-Echebarria, Reference Martín-Echebarria2024a). These landscapes operate as palimpsests, preserving material traces from the First Carlist War (1833–1840) and the Second Carlist War (1872–1876), which are conflicts rooted in divergent visions of Spain: liberal modernity versus the ancien régime (Roldán-Bergaratxea et al., Reference Roldán-Bergaratxea, Martín-Echebarria and Escribano-Ruiz2019; Martín-Echebarria, Reference Martín-Echebarria2024a). These sites thus constitute intergenerational battlefields, embodying the material legacy of successive civil wars (Martín-Echebarria, Reference Martín-Echebarria2024b).
This article presents four recent archaeological interventions on the Iron Belt and offers a preliminary interpretation of its military function and later memorial reconfiguration. While recognizing the limitations of our dataset, we hope to provide a basis for future research within the growing field of archaeological work concerning the heritage of the Spanish Civil War. This increase in academic and public interest has led to formal recognition: in 2019, the Iron Belt, including the nearby English and Artxanda Lines, became the first conflict site in the Basque Country to be granted heritage protection (as a monumental complex), due to its strategic links to the defence of Bilbao (Urkullu Renteria, Reference Urkullu Renteria2019). Institutional commitment to conservation and heritage-making thus reflects a convergence of scholarly, social, and political engagement.
After outlining the historical context of the Iron Belt, our article presents the archaeological interventions we carried out. The discussion focuses on the heritage of the Iron Belt, from its use in the construction of a hegemonic narrative to the controversial cases we have documented.
Construction and Evolution of the Iron Belt
The Spanish Civil War (1936–1939) marked the first major European confrontation between democratic and fascist ideologies (Renshaw, Reference Renshaw2020). International in scope, the conflict saw Franco’s uprising supported by fascist regimes in Germany, Italy, and Portugal, while the Republican side received aid from the Soviet Union and over 46,000 international volunteers from fifty-three countries, forming the International Brigades (Prades Artigas, Reference Prades Artigas, Daura and Blanch2022).
In the Basque Country, the war quickly reshaped territorial control: the region of Alava fell early to Francoist forces, while Biscay and Guipuzcoa initially remained under Republican authority. By late 1936, however, Guipuzcoa had been captured, leaving Biscay as the last Republican stronghold (Figure 1). In response, the Spanish Republic approved the Basque Statute of Autonomy, enabling the formation of the first Basque Government. Among its initial actions were the creation of the Basque Army (Euzko Gudarostea) and the construction of a defensive perimeter around Bilbao. Influenced by First World War military design, the so-called Bilbao’s Defensive Belt was intended to protect the city and its industrial infrastructure (Redondo Rodelas, Reference Redondo Rodelas2005: 44; Santamarina Otaola, Reference Santamarina Otaola2022). The strategy was to prepare Bilbao for a potential siege by Francoist forces, drawing on the city’s historical resilience demonstrated during multiple nineteenth-century Carlist sieges (Martín-Echebarria, Reference Martín-Echebarria2024c).
Figure 1. Map showing the limits of the Iron Belt and the war context in the Basque Country in 1936–1937.
Extending over a perimeter of eighty kilometres, the Bilbao Defensive Belt project was divided into five sectors to facilitate construction (Figure 2). However, from its inception in October 1936, the project faced significant logistical and political obstacles, including shortages of materials, transport, and labour. Internal security was also compromised: among its engineers, Pablo Murga was arrested and executed for espionage in November 1936, while Alejandro Goicoechea defected in February 1937 (Líbano Silvente et al., Reference Líbano Silvente, Salazar Cañarte, Miñambres, Vega López, Zuazo Gibelondo and Olabarrieta2018: 247). Goicoechea provided the Francoists with crucial details, including the fortifications’ plans and status, revealing a poorly fortified sector on Mount Gaztelumendi in Larrabetzu (Líbano Silvente et al., Reference Líbano Silvente, Salazar Cañarte, Vega López, Baizan, Zuazo Gibelondo and Olabarrieta2021: 123), which later became the focus of the offensive (González Portilla & Garmendia, Reference González Portilla and Garmendia1988).
Figure 2. Map showing the different sections of the Iron Belt and the location of the case studies (Muskiz, Somorrostro, Mount Ollargan, and Mount Avril).
In March 1937, following the failure to capture Madrid, Franco’s forces redirected their efforts to the northern front, drawn by the region’s industrial and mineral wealth. The offensive began with an attack on Biscay. Despite the Iron Belt being incomplete, poorly equipped, and defended by demoralized troops (Martínez Bande, Reference Martínez Bande1971: 157–58), the campaign—initially intended to seize Bilbao within three weeks—lasted three months, marked notably by the bombing of Guernica.
Between 11 and 12 June 1937, a major assault was launched on the Belt, beginning with a coordinated bombardment involving 144 artillery pieces and aircraft from the German Condor Legion and Italian Legionary Air Force. This was followed by a successful infantry advance through the weakly fortified Gaztelumendi sector, triggering a general Republican retreat towards Bilbao (Martínez Bande, Reference Martínez Bande1971: 170–74). In response, the Basque Government ordered an evacuation and attempted to delay the city’s fall (Redondo Rodelas, Reference Redondo Rodelas2005: 71). The last line of defence, the Artxanda Line, was breached by 19 June, when Franco’s forces entered the city (Agirreazkuenaga & Urquijo, Reference Agirreazkuenaga and Urquijo2015: 110).
After the capture of Biscay, the new regime took advantage of every aspect of the war to infiltrate daily life on an ideological and cultural level (Rodrigo, Reference Rodrigo2017: 483). It renamed this fortified line the ‘Iron Belt’ to aggrandize the victory at Gaztelumendi (Beldarrain Olalde, Reference Beldarrain Olalde2012: 312). This narrative, reinforced throughout the period of dictatorship, celebrated the strength of the defences and the heroism of Franco’s troops. Over time, the term ‘Iron Belt’ became widely accepted, persisting into the present (Líbano Silvente et al., Reference Líbano Silvente, Salazar Cañarte, Vega López, Baizan, Zuazo Gibelondo and Olabarrieta2021: 124).
Archaeological Interventions in the Iron Belt
The trauma of the Spanish Civil War persisted well beyond the end of the Francoist regime in 1975, sustained by a culture of intentional amnesia (Preston, Reference Preston2018). This ‘pact of forgetting’ dominated public discourse until the early 2000s, when younger generations began demanding a critical reappraisal of this period. Archaeology has played a central role in this process, with a notable increase in investigations across Spain (González Ruibal, Reference González Ruibal2021; Alonso Ibarra & Ruiz Casero, Reference Alonso Ibarra and Ruiz Casero2024).
Conflict archaeology, defined as the study of material traces associated with past conflicts (Landa & Hernández de Lara, Reference Landa, Hernández de Lara, Landa and de Lara2014: 36), emerged in the mid-twentieth century, initially focused on the World Wars. Early descriptive efforts gradually gave way to analytical approaches that consider the wider social, political, and symbolic dimensions of warfare (Pollard & Banks, Reference Pollard and Banks2005). As González Ruibal (Reference González Ruibal, Landa and de Lara2020b) notes, warfare is inherently material, leaving behind tangible traces such as fortifications, weapons, and human remains. This focus on the physical evidence of violence highlights archaeology’s unique capacity to interpret conflict through material culture.
A defining characteristic of conflict archaeology is its intersection with ‘dark heritage’: sites marked by trauma, memory, and contested meanings. Such places, as Landa and Hernández de Lara (Reference Landa, Hernández de Lara, Landa and de Lara2014: 35) argue, are spaces of both remembrance and forgetting. They often become potent symbols within collective memory, transcending historical fact to serve as lieux de mémoire (Nora, Reference Nora1984–92). These sites contribute to the construction of national, ethnic, and political identities, though often filtered through selective memory and shaped by prevailing ideological narratives (Leoni et al., Reference Leoni, Martínez, Porfidia, Ganem, Landa and de Lara2014: 114).
The opposite also occurs: many battle sites are erased, marginalized, or subjected to dememory (Landa & Hernández de Lara, Reference Landa, Hernández de Lara, Landa and de Lara2014: 35). In some cases, this is an intentional strategy, as certain historical legacies conflict with dominant narratives, leading to processes resembling damnatio memoriae, where they are silenced or rendered taboo in public discourse (Ramos, Reference Ramos, Landa and de Lara2014: 27). The evolving narrative of the Iron Belt exemplifies these complexities, embodying tensions between memory and forgetting, marginalization and heritage-making, as well as collective memory versus official history.
The Basque Country is a very dynamic area within this context, with excavations of fighting positions as well as mass graves being promoted (Etxeberria & Calvo Poyato, Reference Etxeberria and Calvo Poyato2020). Many of these efforts concentrated on the Iron Belt, due to its historical significance and the scale of its remains. Investigations at Somorrostro, Mount Avril, and Ollargan were part of broader campaigns focused on uncovering material from the Carlist Wars (Martín-Echebarria, Reference Martín-Echebarria2023). In contrast, the intervention at Muskiz was commissioned by the Basque Government’s Cultural Heritage Centre to assess the preservation of the Iron Belt’s structures for potential inclusion in heritage protection measures. Although these interventions were not initially centred on the Spanish Civil War, the findings exceeded expectations, revealing that the landscape had been profoundly affected across multiple temporal layers. This highlighted the complexity of the battlefield over time, intersecting with earlier conflicts (Martín-Echebarria, Reference Martín-Echebarria2024b).
The excavations, while partial due to the constraints of sampling, should not be taken to obscure the broader complexity of the Iron Belt’s defensive network as a systematic construct and a conflict-driven landscape. While the selected case studies are defined by their focus on the micro-scale, it is precisely the archaeological perspective—centred on spatial interconnectedness and landscape interpretation—that enables the integration of diverse contexts across multiple sectors of the same defensive system. As González Ruibal (Reference González Ruibal, Landa and de Lara2020b: 14) observes, archaeology operates in a space between the individual soldier’s chaos and the general’s strategy, making it crucial for linking micro-level detail with macro-level interpretation.
All interventions, except in Muskiz, formed part of Martín-Echebarria’s doctoral fieldwork. Excavations were funded by the Basque Government’s Department of Culture and the Provincial Council of Biscay, and supplemented with metal detection (Connor & Scott, Reference Connor and Scott1998). Methodological and ethical details are outlined in Martín-Echebarria (Reference Martín-Echebarria2023).
A transgenerational trench in Somorrostro (Abanto-Zierbena)
The Somorrostro valley has traditionally been a military target. During the Second Carlist War (1872–1876), this site saw an important military operation: the Somorrostro campaign. Between February and May 1874 there were three important battles, which ended with two Carlist victories and a final Liberal victory (Palacio Ramos, Reference Palacio Ramos2023).
Archaeological interventions have been carried out in the area since 2010 to recover remains of these military clashes (Arrate et al., Reference Arrate, Olmedo and Astorqui2014). In 2020, our team carried out an archaeological campaign in what appeared to be a Carlist trench from 1874, but analysis of the materials recovered revealed that it was actually a section of the Iron Belt.
Our intervention consisted of two test pits and a metal detector survey. Test pit 1 was located in the centre of the trench. Its base, cut into the rock, was documented at a depth of only 0.4 m. The shallow depth of the trench was surprising, a fact that seems to indicate that the outer wall was reworked using sandbags or some similar type of cover. The finds from the trench consisted of a set of twelve complete Mauser cartridges and a spring comb magazine guide of the same system.
Test pit 2 was also located in the centre of the trench, where a semi-circular structure was suspected. In the vegetation cover, five poorly preserved cartridge cases were found. We interpreted these casings as .577 Snider cartridges, i.e. British ammunition used by the Carlists in 1872–1876. After removing several strata with hardly any material, we documented stratigraphic unit 203, a level that filled the entire structure and reached a depth of between 1.60 and 1.86 m, which made it difficult to excavate its lower parts. Stratigraphic unit 203 contained the highest number of finds. In the upper part, four fragments of artillery projectiles used by the Liberals were recovered. Further down, in what we have interpreted as the level of use, three elements of the 7.92 × 57 mm Mauser system, several 29 × 23 mm cases, numerous barbed wire fragments, several fragments of tin cans, and the base of an anisette bottle were recovered (Figure 3). All these materials are attributed to the Spanish Civil War.
Figure 3. Finds from Somorrostro. 1) Base of an anisette bottle; 2) a collection of 7.92 × 57 Mauser cartridges found in the test pit; 3) fragments of Krupp artillery; 4) possible .744 Snider cartridge cases from the Second Carlist War.
The test pits have an inverted stratigraphy, with older materials (Carlist cartridges and Liberal grenades) found at the top and more modern finds (Mauser systems, barbed wire, and anisette bottle) at the base. The most plausible explanation is that the Basque Army re-excavated an original Carlist trench as part of the Iron Belt’s sector 1. When the Basque Army ‘re-built’ this trench, it altered the context of the Second Carlist War stratum, and its materials were re-deposited on the surface. The remains of tin cans and the base of an anisette bottle, serve as evidence that the military consumed food and alcohol.
Afterlives of the machine-gun nests and concrete galleries in Muskiz
Like Somorrostro, the Muskiz case study belongs to sector 1 of the Iron Belt. This sector did not see major actions during the Spanish Civil War, but it was used to control access to the port of Bilbao. In 2018, the regional government’s decision to protect the Iron Belt in law resulted in the Basque Cultural Heritage Centre being asked to conduct an archaeological study in the Muskiz coastal area. The Basque Army had originally built two machine-gun emplacements and a concrete bunker embrasure gallery in this area. As the remains of these defences were severely damaged by the construction of a residential complex in the early 2000s, the archaeological intervention was based on assessing the feasibility of including these remains in the legal document (Escribano-Ruiz et al., Reference Escribano-Ruiz, Santamarina, Herrero, Pozo and Martin Etxebarria2018).
The archaeological team found that one of the machine-gun positions was completely destroyed (Figure 4: 1 and 2). A mechanical excavator had probably dismantled the structure and piled the remains on top of it. In another sector, however, it was possible to document a rectangular, two-storey machine-gun emplacement. The upper structure, without a roof, would have housed the machine-gun, and the lower one, under the firing plateau, would have served as an ammunition depot. The structure’s firing range was oriented towards the Arena beach. From this emplacement, a 15-metre-long concrete gallery (Figure 4: 3 and 4) led off to the north-west, its roof dismantled. Nonetheless, a pair of gun ports remained. Two construction phases, represented in the negatives of the wooden planks of the formwork, could be seen in the structure’s vertical walls. A preserved footprint on the floor of the gallery was also noteworthy. The finds included two iron stakes with several notches for passing barbed wire from inside the emplacement (Escribano-Ruiz et al., Reference Escribano-Ruiz, Santamarina, Herrero, Pozo and Martin Etxebarria2018: 363–64).
Figure 4. Defensive structures in Muskiz. 1) Machine-gun emplacement; 2) remains of the destroyed concrete gallery and pile of debris: 3–4) excavation of the gallery; 5) current state of the area, with new urban development.
The site was reused after the war. Aerial photographs show that a very simple, shanty-like housing complex was built in the 1950s. During excavation, we documented the original tiled floor of this interior dwelling, as well as the concrete access road. This structure was attached to the northern entrance of the shooting gallery, thus combining the former military installations with the dwelling. Oral testimonies revealed that a single male inhabited this space between 1950 and 2010 (Santamarina Otaola, Reference Santamarina Otaola2022: 335). In 2007, a construction company destroyed this dwelling to build a residential complex, but this was left unfinished because the property bubble burst a year later. The company became insolvent and the architectural remains of the Iron Belt were razed and backfilled; they remained forgotten, marginalized until the 2018 intervention (Escribano-Ruiz et al., Reference Escribano-Ruiz, Santamarina, Herrero, Pozo and Martin Etxebarria2018: 366–67). This area was eventually not included in the Iron Belt protection decree and today a new residential complex is nearing completion (Figure 4: 5).
A rectilinear trench on Mount Avril (Bilbao)
Mount Avril is one of the main heights of the Artxanda range, a low mountain range that surrounds the city of Bilbao to the north (Figure 2). During the Spanish Civil War, the Artxanda Line was built in this area as a second (and last) line of defence against the possible fall of the Iron Belt. The Artxanda Line was also protected by the Iron Belt decree (Urkullu Renteria, Reference Urkullu Renteria2019). From 2010 onwards, various archaeological interventions were carried out on these heritage remains, first on Mount San Pablo (Martínez Velasco & Valdés García, Reference Martínez Velasco and Valdés García2014) and later on Mount Avril (Telleria Sarriegi, Reference Telleria Sarriegi2016, Reference Telleria Sarriegi2017).
In the Mount Avril area, Etor Telleria Sarriegi excavated a section of a trench dating from 1937 (Figure 5: 2). As the trench had been cut directly into the rock, this entailed considerable excavation work. Some of the slabs extracted had been placed at the front of the trench as a parapet; they had also been used to reinforce the back wall to prevent possible cave-ins. Gravel was used to improve the seating of the parapet, securing the flatter slabs (Telleria Sarriegi, Reference Telleria Sarriegi2016: 273). The archaeological intervention revealed that the form of the trench was rectilinear, which is unusual in Spanish Civil War contexts (González Ruibal, Reference González Ruibal2020a: 121). The rectilinear shape of the trench indicates that it was adapted to the topography of the area, but it rendered the positions extremely vulnerable to artillery barrages.
Figure 5. 1) Plan of the fort of Mount Avril in 1874–1876 (Saudino y Labaig, 1876); 2) excavated and reconstructed trench of the Spanish Civil War period; 3) .43 Spanish Remington cartridge cases from the Second Carlist War recovered in the area; 4) 7.92 × 57 mm Mauser cartridge cases related to the Spanish Civil War. (1) reproduced by permission of Ministerio de Defensa - Instituto de Historia y Cultura Militar - Archivo General Militar de Madrid.
The few finds recovered all relate to military equipment. Inside the trench, Mauser cartridge cases (Figure 5: 4) were recovered on its use level. However, in the phases related to the construction of the trench, the team recovered .43 Spanish Remington ammunition (Figure 5: 3). This ammunition was adopted by the Spanish army in 1871 and became popular during the Second Carlist War. Telleria Sarriegi (Reference Telleria Sarriegi2016: 274) first proposed that these represented archaic material used by the Spanish Republic, whose fighters were always in need of ammunition, at the beginning of the Spanish Civil War. Later archaeological interventions conducted by Martín-Echebarria demonstrated, however, that these remains were related to a combat in May 1874, between Carlist and Liberal troops during the Second Carlist War (Saudino & Labaig, Reference Saudino and Labaig1876; Martín Echebarria, Reference Martín-Echebarria2024b: 305). As at Somorrostro, fortification works carried out during the Spanish Civil War altered the previous Carlist context, so that after the oldest remains were re-deposited on top of the more recent material.
Remnants of final combat in Mount Ollargan
Mount Ollargan lies on the opposite side of the trenches on Mount Avril. This is a strategic point located in the southern part of Bilbao, at the intersection of the roads leading to Guipuzcoa and Alava. Due to its privileged location, the mountain was fortified on different occasions since the early nineteenth century. The construction of a large fort by the Carlist army (Figure 6: 1 and 2) after the Second Carlist War is noteworthy (Escondrillas, Reference Escondrillas1876: 21; Fernández Gómez, Reference Fernández Gómez1876).
Figure 6. 1) Plan of the Carlist fort of Ollargan in 1876 (Fernández Gómez, Reference Fernández Gómez1876); 2) satellite image of the Carlist fort in 1976; 3) set of 7.92 × 57 mm Mauser cartridges; 4) 88 mm artillery shell fragments. (1) reproduced by permission of Ministerio de Defensa - Instituto de Historia y Cultura Militar - Archivo General Militar de Madrid.
Figure 7. Mount Ollargan. 1) Set of 7.92 × 57 mm Mauser magazine guides; 2) set of 7.92 × 57 mm Mauser cartridge cases; 3) magazine guides found during excavation; 4) distribution map of the Spanish Civil War materials recovered on Mount Ollargan.
This nineteenth-century fortification was the subject of an archaeological intervention in 2022. The intervention strategy included the excavation of several sondages, and a metal detector survey of the fort and the entire surrounding area.
Among the finds relating to the Spanish Civil War, the largest group included 7.92 × 57 mm Mauser cartridges (Figure 6: 3; Figure 7: 1–3), accounting for sixty per cent of the total assemblage: fifty-five cartridge cases, all but one of which were percussion casings, thirty-one magazine guides, and six complete cartridges. The second largest group consisted of seven 7,7 × 56 British R cartridge cases. The team also found a Mauser rifle muzzle cover, a piece used to cover the muzzle of the barrel and protect it from dirt. Finally, several fragments of artillery shells and shrapnel indicate that the area suffered an artillery attack during the Spanish Civil War. An almost complete Garrido fuse for 70- and 75-mm artillery was also found. Finally, material relating to the Second Carlist War was also recovered, but in smaller quantities.
Most of the shell casings and comb-guides are clustered on the parapet of the fort in its western sector (Figure 7: 4), suggesting that one or more shooters fired from this position over a sustained period. As most of the ammunition was German-made 7.92 ×57 mm Mauser ammunition, we believe that these were infantrymen from the Francoist side. The cartridge cases were percussion-perforated, and the comb guides thrown between them, which corresponds to whole magazines being emptied from this position. This reinforces our interpretation of a sustained firing position over time. Artillery elements from the Spanish Civil War, consisting of several fragments of 88 mm Krupp and grenade type fuses, as well as shrapnel (Figure 6: 4) are also concentrated on this parapet. A second group of shrapnel fragments, to which we cannot assign a date, was also distributed inside and outside the fort.
This material is evidence of the heavy fighting that took place in this position on 15–17 June 1937: the Francoist troops attacked Mount Ollargan with the intention of surrounding Bilbao from the south and completing the encirclement of the city. The fighting was intense and went on for several days, with several attacks and counterattacks on both sides (Alonso, Reference Alonso1999).
The materials recovered indicate two phases of the Francoist offensive. First, the artillery shelled the Republican positions heavily. Then the infantry advanced to dislodge the resistance and take the position. It should be noted that the recovery of several fragments of fuse fragments for 88 mm Krupp grenades, the famous German anti-aircraft gun, could be a testimony of a possible dogfight aerial combat in this area, although it could also reflect the use of such guns against ground positions.
Ninety-nine per cent of the markings on the cartridge cases were identified as German, indicating that the Francoist troops were quickly and regularly supplied with new and quality ammunition by Nazi Germany. Data also show a high level of standardization of the Francoist army as almost all the ammunition used is of the same calibre (7.92 × 57 mm), which facilitates the supply of ammunition. The complete opposite would have applied on the Republican side, where the plurality of weaponry was the norm (González Ruibal, Reference González Ruibal2020a: 61).
Discussion
Bilbao’s Iron Belt is a milestone in the military architecture of the Spanish Civil War. It is a highly developed and complex defensive line, with a multitude of military elements of different functions and types. It therefore formed a vast conflict landscape that was mythologized by both sides of the conflict.
In addition to its purely historical and archaeological value, the Iron Belt has an important memorial component as it acquired a mythical status since its construction. On the one hand, on several occasions, the Basque Army abandoned positions that were easier to defend because of its confidence in the Iron Belt (Agirreazkuenaga & Urquijo, Reference Agirreazkuenaga and Urquijo2015: 122), despite some sections being only partially constructed by June 1937 (García Uribe & Casado Zárate, Reference García Uribe and Casado Zárate2014; Ayán Vila & García Rodríguez, Reference Ayán Vila and García Rodríguez2016). This idea of invincibility did not entirely disappear after the war, as Basque nationalists in exile continued to uphold the notion of the resistance of the Basque soldiers (gudaris) (Martínez Rueda, Reference Martínez Rueda2022). Additionally, the recent process of memorialization of the fortified line has revitalized the idea of its strength and resilience. Francoists, on their side, used their victory on the Iron Belt as a propaganda tool to reinforce their regime. Among its propaganda, not only did they rename this structure the ‘Iron Belt’ but also organized tourist excursions and planned a museum on this fortified line (Brena Alonso, Reference Brena Alonso2016).
Archaeology helps us to explore such complex and politicized issues (Ayán Vila & Santamarina Otaola, Reference Ayán Vila and Santamarina Otaola2024). Conflict archaeology (González Ruibal, Reference González Ruibal2020a) highlights the dual nature of the Spanish Civil War, a testing ground for new warfare methods, such as the Blitzkrieg tactics used by the Legion Condor (Cardona, Reference Cardona2007), but also a continuation of more traditional combat. The prevailing model of combat mirrored that championed by the victors of the First World War, notably influenced by the French army, given its geographical proximity and cultural affinity (Ayán Vila & García Rodríguez, Reference Ayán Vila and García Rodríguez2016; Marqués Bautista & Sáez Rodríguez, Reference Marqués Bautista and Sáez Rodríguez2022). The defensive strategy of the Iron Belt can be interpreted as a regional adaptation of the Maginot Line (Smart, Reference Smart1996; Jackson, Reference Jackson, Leitz and Dunthorn1999). The reuse of earlier defensive positions from the Carlist Wars (the trenches at Somorrostro and Monte Avril) further illustrates the Basque Army’s adherence to the static warfare model characteristic of the First World War.
The four interventions discussed here highlight the shortcomings in the design and implementation of the Iron Belt. Despite being a military strategy tailored to the region’s rugged terrain, its scale proved overly ambitious for the newly formed Basque Army, which lacked the manpower and resources to construct and defend such a vast perimeter. The Iron Belt reflected an outdated military model, with its weaknesses exploited by the Francoist forces, who held a significant advantage, particularly in aviation. The rise of aviation and Blitzkrieg tactics in European warfare marked a pivotal shift: a few years later, the Maginot Line would similarly fail to withstand the German assault during the Second World War (Passmore, Reference Passmore2025). Nonetheless, the Spanish Republic continued to fortify its territory with other significant defensive lines (Schnell Quiertant, Reference Schnell Quiertant2012), such as the Cinca Line between Aragon and Catalonia and the XYZ Line in Castellón, probably because pursuing any other strategy was unfeasible given the limited resources and capabilities.
The superiority of Franco’s offensive left its mark on the landscape (Alonso Ibarra & Ruiz Casero, Reference Alonso Ibarra and Ruiz Casero2024): both the weaponry and structures documented in our interventions attest to the lack of preparation of the Basque Army. Thus, the mythologized image of the Iron Belt’s strength, constructed and sustained for decades—during the early years of the Franco regime and, more recently, by nationalist governments following a prolonged period of neglect of the Spanish Civil War heritage—can finally be debunked.
After the capture of Biscay, Franco’s regime decided to bestow heritage value on this battlefield by erecting crosses in memory of the fallen at the most significant geographical locations (Ayán Vila & García Rodríguez, Reference Ayán Vila and García Rodríguez2016; Rolando Rico & Peña-Muñoz, Reference Rolando Rico and Peña-Muñoz2021; Del Arco Blanco, Reference Del Arco Blanco2022). In the late twentieth century, however, the remains of the Iron Belt fell gradually into oblivion once its message was no longer useful to Francoism. Some of these remains were abandoned and even looted: the concrete decks were dismantled to sell their iron as scrap (Líbano Silvente et al., Reference Líbano Silvente, Salazar Cañarte, Miñambres, Vega López, Zuazo Gibelondo and Olabarrieta2018). This long period of abandonment resulted in ruined and backfilled structures invisible ion the landscape.
From the 2000s onwards, at a time when the archaeology of the Spanish Civil War was taking off, the first academic works on its defensive architecture started to be published (Association Sancho de Beurko, 2008; Tabernilla, Reference Tabernilla2010). However, before the advent of such professional research, it was the non-academic sphere (memorial associations, volunteers, groups of amateur historians, and town councils) that pioneered the identification, characterization, and rediscovery of the Iron Belt (Herrero Acosta & Ayán Vila, Reference Herrero Acosta, Ayán Vila and Urtizberea2016: 103). They promoted it by compiling the first inventories of Iron Belt remains and creating a small interpretation centre in the town of Berango (Miñambres Amézaga, Reference Miñambres Amézaga2020). The first archaeological projects took place later, conducted by teams from both the university and the professional spheres, providing greater historical and archaeological knowledge not only about the Iron Belt but also about the Spanish Civil War in Biscay. Of particular importance is the growing tendency among heritage professionals to move beyond the mere production of academic knowledge and engage with wider society. As a result, activities linked to dissemination, communication, and social engagement (e.g. public lectures, guided tours, exhibitions, and open days) have become increasingly important. This approach was adopted in the case studies discussed here and received very positive responses (Martín, Reference Martín2022).
The Iron Belt shows the dichotomies, divergences, controversies, and changes in status that can be associated with a heritage landscape of such symbolic importance (Farrell-Banks, Reference Farrell-Banks2022). On a social level, there is a significant emotional identification with the Iron Belt, reflected in the erection of monuments to commemorate it, the staging of historical re-enactments and guided tours, and the creation of exhibitions. All in all, these structures have acquired heritage status and form an integral part of a new heritage landscape (Pollard & Banks, Reference Pollard and Banks2010). Despite this generally positive situation, there are also controversial examples.
The case of Muskiz is one such controversial case: the Iron Belt structures were destroyed to build a housing complex that was cancelled as a result of the 2008 financial crisis (Escribano-Ruiz et al., Reference Escribano-Ruiz, Santamarina, Herrero, Pozo and Martin Etxebarria2018), thereby transforming the area from a monumental landscape into a non-landscape. The halt in construction added a further historical stratum, as a neo-ruined landscape emerged from this absence (Santamarina Otaola, Reference Santamarina Otaola2022: 336). This final layer, however, has since been erased with the resumption of the original urban development. Currently, there are no material remains of the Iron Belt in this sector. What persists is the memory held by the local community: a recollection of a once-existent heritage and conflict landscape that has now been entirely eradicated. This mirrors the dynamic seen with the mass graves of the Spanish Civil War: in the absence of physical evidence, it is oral memory that highlights the trauma and forms of remembrance that may not be fully represented by the prevailing investigative agenda (Renshaw, Reference Renshaw2020). This act of heritage destruction went unpunished as no law designed to protect wartime heritage existed until very recently, a paradox as this heritage was highly mythologized: as Barreiro Martínez (Reference Barreiro Martínez2014: 305–06) points out, ‘heritage is a field of conflict that … materializes the existing social contradictions’ (our translation).
Conclusions
The four archaeological interventions presented in this article reveal the weakness of the fortified line known as Iron Belt within the context of the Spanish Civil War. Our findings reveal that the Basque Army was inadequately prepared and had an outdated defence strategy in the face of the advent of aerial warfare. Our interventions debunk the notion of ‘resistance’ and ‘invincibility’ associated with the Iron Belt, which was promoted by both the Republicans and the Francoists. It is thus an example of how archaeology can help us to gain new information in contested and socially mythologized contexts.
Our investigations have also thrown light on the controversies surrounding the protection/or lack of protection of the Iron Belt heritage over the last eighty years. The Franco regime briefly appropriated the Iron Belt’s symbolism through commemorative practices, before its significance faded and many structures fell into disrepair or were deliberately dismantled. From the early 2000s, local associations and municipalities, rather than academic institutions, led efforts to document and preserve what remained, later joined by university-led archaeological projects. These initiatives have expanded the scholarly understanding of the Spanish Civil War in Biscay and promoted the social dissemination of its heritage through public engagement activities.
Despite these efforts, the Iron Belt remains a contested and vulnerable heritage landscape. In cases such as Muskiz, the destruction of fortifications for speculative urban development illustrates the precarious status of the wartime heritage in the absence of solid legal protection measures. The result is a landscape of erasure, where community memory endures despite the loss of physical traces. This parallels the dynamics surrounding the Spanish Civil War’s mass graves, where oral testimony sustains memory in the absence of actual remains (Renshaw, Reference Renshaw2020). Ultimately, the Iron Belt exemplifies how conflict heritage reflects broader social tensions and unresolved historical legacies.
Acknowledgements
The archaeological interventions were financed by public institutions through competitive grants. Specifically, they were funded by the Provincial Council of Biscay (Orden Foral de La Diputada Foral de Euskera, Cultura y Deporte 1545/2022; details at: https://www.bizkaia.eus/lehendakaritza/Bao_bob/2022/08/18/I-748_cas.pdf?hash=61c76905093e2d819422bdd16475ad6a) and by the Cultural Heritage Centre of the Basque Government (Resolución del Viceconsejero de Cultura, 109/2020; details at: https://www.euskadi.eus/bopv2/datos/2020/01/2000109a.pdf). The project also received the support of a fellowship from La Caixa Foundation (ID 100010434; fellowship code LCF/BQ/DR21/11880004). Open Access funding was provided thanks to the CSUC agreement with Cambridge Univeristy Press. Data can be made available on request.
Open access
