Until 2019, of the 125 archaeological sites cataloged in the Bay of Algeciras, only four were underwater. And of those four, barely one was a shipwreck: the wreck of the Ballenera, a 17th-century ship with Italian ceramics on board. The rest of the bay's bottom —one of the most trafficked maritime enclaves on the planet since ancient times— was, for archaeology, a blank map. No one had studied it systematically since the mid-1980s.
It is no longer so. The Herakles Project, led between May 2020 and March 2023 by researchers Felipe Cerezo Andreo and Alicia Arévalo González from the University of Cádiz, has identified 151 new underwater archaeological sites and documented in detail 34 wrecks dating from the 5th century BC to the 20th. The results, recently published in the proceedings of the I Ibero-American Congress of Underwater and Nautical Archaeology (Editorial UCA, 2025), outline for the first time the submerged history of a place that for millennia has been a gateway between the Mediterranean and the Atlantic, between Europe and Africa.
The most remarkable thing: the vast majority of these finds were less than ten meters deep. Some were a stone's throw from the beach. In the first diving campaign, in just three weeks, 17 new sites appeared. In the following months, diving from the shore without the need for a support vessel and at depths between four and eight meters, the team located more than 80 archaeological sites exposed on the seabed. The abundance of remains was such that researchers had to adopt a selective strategy on the fly: document as much as possible in the least amount of time and with the least impact on the remains.
By the time the project closed its field phase in March 2023, the count had risen to 151 sites: 124 classified as wrecks, 7 historical anchorages, and 20 isolated objects —anchors, ceramic fragments, rigging elements, and other evidence of nautical activity—. Of all of them, 34 wrecks were documented with detailed techniques: underwater photogrammetry, 360° videos, three-dimensional modeling, and digital mapping. Only one of the 151 sites was considered necessary to excavate.
The Bay of Algeciras is neither a forgotten corner nor a minor enclave. It is home to one of the ports with the highest container traffic in the entire Mediterranean, neighboring Gibraltar and the scene of centuries of naval conflicts for control of one of the world's most important maritime routes. Ancient cities such as Carteia or Iulia Traducta were established along its shores. During the Middle Ages, it served as a border and entry point to the Iberian Peninsula. In modern times, it was a permanent battlefield between European powers disputing control of the Strait. Numerous studies have highlighted the importance of this environment focusing on terrestrial archaeology, but the heritage lying beneath its waters had been systematically ignored. The Herakles Project starts from a premise that seems obvious but that no one had put into practice: it is not possible to build the history of Algeciras without looking at what lies beneath its sea.
From the 5th century BC to the 20th: what the wrecks tell
The shipwrecks found form a catalog that spans practically all of maritime history in the Strait, from Punic antiquity to the contemporary era. 24% of the 151 identified sites have been studied and documented in sufficient detail to know their period of construction or use, their typology, and their state of conservation. The rest is awaiting future campaigns.
The oldest wreck is the Timoncillo I, dated to the 5th century BC, in the midst of the Punic period. Alongside it, six other sites from the same era confirm that the bay was an active naval transit area long before the arrival of Rome. They are testimonies of Phoenician-Punic navigation of which there had been indirect evidence through terrestrial archaeology and written sources, but lacked direct material evidence on the bay's bottom.
From the Roman period, 23 sites have been identified, the most numerous chronological group. Several of them concentrate around the ancient Carteia, the Roman colony that arose at the mouth of the Guadarranque River and was one of the most important ports of Bætica. The area between that mouth and Puente Mayorga has proven to be an anchorage in continuous use since at least the 4th century BC to the present day: more than 2,400 years of uninterrupted activity. Surveys conducted with differential GPS allowed for precise georeferencing of a large amount of archaeological material scattered across the seabed —ceramics, anchors, cargo remnants— whose chronological variety outlines a sequence of use that has practically no interruptions. It is one of the anchorages with the longest historical trajectory in the entire bay and, probably, of the entire Cádiz coastline. Two late Roman wrecks have also been confirmed, including El Anclote, which has been the subject of a monographic article published in the same volume of proceedings. These findings fill an important chronological gap: the transition between late antiquity and the early Middle Ages is one of the periods least represented in the underwater archaeology of southern Iberia.
Four wrecks correspond to the medieval period. Among them stands out a particularly valuable find: a possible wreck of Merinid chronology located in the El Rinconcillo area. The Merinids —the Berber dynasty that ruled the Maghreb between the 13th and 15th centuries— used the Strait as a gateway to al-Andalus in their military and commercial interventions. The presence of a wreck from this period in the Bay of Algeciras has full historical coherence, but from an archaeological point of view, it is extraordinary: there are hardly any known remnants of Merinid vessels in any seabed. A detailed study, which the researchers place among the priorities for future projects, could shed light on a practically unknown chapter of the history of shipbuilding and maritime traffic in medieval Western Mediterranean.
The most numerous group of wrecks by period is from the modern era: 24 shipwrecked vessels between the 16th and 18th centuries, of various nationalities and typologies. Many are directly or indirectly linked to the conflicts over control of the Strait and Gibraltar. The British seizure of the Rock in 1704, the successive Spanish attempts to reclaim it —including the Great Siege of 1779-1783—, naval battles between European powers, and the relentless smuggling traffic that unfolded in these waters for centuries left a trail of shipwrecks that historical archives document profusely, but which had until now practically not been located underwater. The Rinconcillo VIII and Puente Mayorga II, both from the 17th century, and Arroyo de los Patos II, from the 18th, are some of the most significant wrecks from this period.
But the find that the researchers themselves qualify as exceptional is the wreck Puente Mayorga IV, a gunboat from the late 18th century preserved at very shallow depth. It was the only site of the project where intrusive methodology was employed —that is, archaeological excavation in the strict sense—, and there are good reasons for it. Gunboats were light vessels, with a shallow draft, designed to operate in coastal waters carrying one or two pieces of heavy artillery. Spain used them extensively during the sieges of Gibraltar and in other naval operations of the 18th century. However, despite their tactical and historical importance, very few archaeological remains of them are preserved worldwide. Puente Mayorga IV is, therefore, a significant find that transcends the local.
The team conducted a complete systematic excavation of the wreck: manual drawing to scale of the entire naval structure, photogrammetric documentation, 3D modeling, and taking wood samples for anatomical identification and dendroarchaeological studies —a technique that allows dating wood by analyzing growth rings and, in some cases, determining the geographic origin of the material with which the vessel was constructed—. The entire process was recorded in 360° videos intended for both research and public dissemination. Preliminary results point to a vessel of Spanish construction from the late 18th or early 19th century, which would place it in the context of naval operations between the last sieges of Gibraltar and the Napoleonic Wars.
What the archives say: 2,000 shipwrecks and a lost archive
The fieldwork was complemented by documentary research that, on its own, constitutes a considerable contribution to the knowledge of maritime history in the Strait. The team constructed several interrelated databases that gather information from archives, museums, historical photographs, and ancient cartography.
The largest of these is that of shipwrecks: more than 2,000 recorded naval accidents in the Algeciras area between the late 18th century and World War II. A figure that dispels the exclusively military image often projected about the Strait: 81% of those shipwrecks corresponded to merchant vessels, not military ones. The bay functioned, above all, as a commercial space where coastal routes, transatlantic crossings, and traffic between the two shores of the Mediterranean converged. By flags, 36% of the shipwrecks were British —which aligns with the naval presence of the power in Gibraltar—, 25% Spanish, and 8% American.
However, there is a notable documentary gap. The 16th and 17th centuries have barely any records of shipwrecks in the area, a void that researchers attribute to the loss of the Gibraltar Archive after the British takeover of 1704. This absence conditions the historical reading of the bay: precisely the centuries in which some of its most intense transformations occurred are the least documented.
The team also cataloged 128 pieces of historical cartography —38 nautical charts, 66 plans, and a series of drawings and coast profiles—. 88% are from the 18th century, prior to the major industrial transformations of the bay and to modern dredging, which makes them documents of enormous value for reconstructing what the coast looked like before port industry reshaped it. Some of these plans have been georeferenced using geographic information systems to overlay the historical coastline with the current one and measure the extent of the alterations.
The historical photography database includes more than 280 records: aerial images, photographs of port spaces during the industrial period, documentation of dredging works. A particularly valuable resource turned out to be the underwater photographic archive from the 1970s and 1980s, provided by Félix Rodríguez Lloret, a pioneer in underwater exploration and the protection of the cultural underwater heritage of the bay. Rodríguez Lloret's images showed anchors, amphorae, and various archaeological sites that no one had revisited in decades. Their digitization allowed the Herakles team to relocate sites whose exact location had been lost and, in the process, document the changes that the marine environment has undergone due to industrial activity, including the devastating expansion of the invasive alga Rugulopteryx okamurae, which is transforming the bay's bottoms.
Finally, the team reviewed the reports of the 97 previous underwater archaeological interventions conducted in the bay. The analysis of these documents —whose access, despite being public documentation, presented considerable bureaucratic difficulties— is revealing. Of the total interventions, 52% were negative: they found nothing. Those that did yield results (48%) mostly came from the monitoring of port dredging (42%): that is, they were accidental findings during works, not the fruit of planned research. Geophysical surveys only contributed 19% to positive findings and archaeological soundings 15%. The record of 58 port works documented by the project, with its associated mapping integrated into a GIS, has allowed for overlaying dredged areas with the intervention reports, and the conclusion is troubling: in areas like the old maritime front of Algeciras or the surroundings of Isla Verde —now occupied by port facilities gained from the sea—, the absence of findings suggests that the remains were destroyed before anyone could document them.
A heritage that is unearthed on its own and that no one protects
That practically all of the findings from the Herakles Project are less than ten meters deep is not casual. Researchers explain it as a symptom of a larger problem: port works and climate change are altering sediment transport dynamics in the bay, exposing remains that had been buried for centuries beneath the seabed and protected by it.
Algeciras houses one of the ports with the highest traffic volume in the Mediterranean. Decades of dredging, filling, and infrastructure construction have radically transformed the bay. The Guadarranque River, whose mouth was the heart of ancient Carteia, has seen its course and sedimentary dynamics altered. Entire coastal areas have disappeared beneath port grounds. And the result of all these interventions is that wrecks and archaeological materials that had remained stable for centuries, protected by layers of sand and mud, are becoming exposed to the action of water, biological erosion, and mechanical impacts. This explains why so many remains appeared in such shallow waters and so close to the beach: it is not that the ships sank there, but that the sediment covering them has disappeared.
While it is true that the bay has the protection figure of Archaeological Servitude —which in theory protects the heritage that potentially exists beneath its waters—, in practice, the researchers warn, the deterioration is notable. Underwater heritage is subjected to high-impact risks: port activity (dredging and anchoring), industrial activity (infrastructure works), tourism (degradation and pillaging due to ignorance), urban development, and the changes that these actions provoke in the marine environment.
The diagnosis is worrying. According to the study, 56% of the documented heritage is in good conservation condition, but the remaining 44% needs immediate attention: study, protection, and, in some cases, urgent intervention. And this counting only what has been able to be examined, which is barely 23% of the bay's surface area, the strip closest to the coast.
The deep areas —the remaining 77%— remain unexplored and are subjected to another threat that researchers point out with particular concern: the anchoring activity of large freighters and ships arriving in Algeciras and Gibraltar. These ships anchor at depths between 60 and 90 meters with heavy chains and anchors weighing over twenty tons that drag along the bottom during each anchoring and raising maneuver. If there are archaeological remains at those depths —and historical logic and the database of more than 2,000 shipwrecks suggest that there are—, the impact of that activity could be irreversible. It is a heritage that could be being destroyed without anyone knowing.
In light of this situation, the Herakles Project has shared the collected data with the institutions responsible for this heritage: the Center for Underwater Archaeology of the Andalusian Institute of Historical Heritage, the Port Authority of the Bay of Algeciras, Maritime Captaincy, the Commonwealth of Municipalities of the Campo de Gibraltar, the City Council of Algeciras, the Civil Guard, and the Navy. Researchers hope that the information generated by the project will serve to create risk layers that indicate the degree of urgency in intervention over each site and allow for designing effective management and protection strategies.
A new project, called Port-SUB and focused on the intelligent management of underwater cultural heritage in port areas of Andalusia, has been born directly from the threats identified during Herakles. It has been presented to the aid call of the Complementary Plan for Marine Sciences, within the Recovery, Transformation and Resilience Plan.
At the same time, the team has designed a pioneering pilot project in Andalusia to create a visitable archaeological site in the Getares area, as a starting point for a future underwater archaeological park. The idea is to turn part of that submerged heritage into a sustainable tourist resource, involving recreational diving companies in the area and local stakeholders. The outreach activities conducted during Herakles have included "dry diving" experiences with virtual models and immersive videos, as well as the publication of 3D models of real archaeological pieces on open platforms like Sketchfab, where anyone can virtually explore the remains documented on the bay's bottom.
The Herakles Project has also served as a training space: students from the Master's program in Nautical and Underwater Archaeology at the University of Cádiz have completed their internships in the campaigns, and several master's theses and doctoral dissertations have been developed under the auspices of the research.
Researchers acknowledge that what has been done so far is only the beginning. There is still much to analyze in detail for each of the 151 identified sites and to address the deep areas of the bay, which constitute the majority of its extent. Among the wrecks they consider priority for future studies through archaeological soundings are the Timoncillo I (5th century BC), the Guadarranque III (1st century BC), the Merinid wreck of El Rinconcillo, Rinconcillo VIII (17th), Arroyo de los Patos II (18th), Puente Mayorga II (17th), and Puente Mayorga IV (18th-19th). Their detailed analysis could provide unprecedented information about trade, maritime traffic, and naval technology from periods for which archaeological knowledge is still very scarce.
But the underlying message of the study transcends the list of findings. Building the history of Algeciras without taking into account what lies beneath its waters is, they conclude, impossible. One cannot understand the role the sea has played in the development of this area without deeply knowing its coast and its evolution, the articulation of navigation, and its submerged heritage. The remains scattered across the bay's bottom —not only the exceptional wrecks but also the more modest fragments— tell stories of dangers for navigation, safe places, transit areas, anchoring spaces, and everyday life aboard. They are the traces of the people who have navigated the shores of the Strait for twenty-five centuries. And if what remains is not documented and protected, it will be lost forever.
"The sea is full of stories, stories of people who moved in boats, some of which sank," the authors write. "Studying, protecting, and interpreting these sites is the responsibility of underwater archaeologists and colleagues from other fields in an interdisciplinary effort. Making them known to the public is the responsibility of all of us."
The study "Between the Columns of Hercules, underwater archaeology of a privileged space. The Bay of Algeciras. Initial results of the Herakles Project" is signed by Felipe Cerezo Andreo, Raúl González Gallero, Carlota Pérez-Reverte Mañas, Soledad Solana Rubio, Alberto Salas Romero, Nicolás C. Ciarlo, Elisa Fernández Tudela, Habana Sánchez Muñoz, José Bettencourt, Marina Goñalons Lapiedra, Sergio José López Martín, and Alicia Arévalo González. It has been published in the Proceedings of the I Ibero-American Congress of Nautical and Underwater Archaeology (CIANYS 2021), edited by Felipe Cerezo Andreo, Carlota Pérez-Reverte Mañas, and Soledad Solana Rubio (Editorial UCA, 2025, ISBN: 978-84-9828-995-4). The Herakles Project was co-financed by the Operational FEDER Program 2014-2020 and the Ministry of Economy, Knowledge, Enterprises and University of the Junta de Andalucía (ref. FEDER-UCA18-107327).