Archaeologists have discovered an ancient submerged stone bridge in Genovesa Cave on Mallorca, the main island of the Balearic Archipelago and the sixth largest in the Mediterranean Sea. The discovery suggests that humans settled the western Mediterranean much earlier than previously believed.
The 5,600-year-old submerged stone bridge in Genovesa Cave, Mallorca, Spain. Image credit: R. Landreth.
Reconstructing early human colonization of the Balearic Islands in the western Mediterranean is challenging due to limited archaeological evidence.
By studying a 7.7-m (25-foot) submerged bridge, University of South Florida’s Professor Bogdan Onac and his colleagues were able to provide compelling evidence of earlier human activity inside Genovesa Cave.
“The presence of this submerged bridge and other artifacts indicates a sophisticated level of activity, implying that early settlers recognized the cave’s water resources and strategically built infrastructure to navigate it,” Professor Onac said.
Located near Mallorca’s coast, Genovesa Cave has passages now flooded due to rising sea levels, with distinct calcite encrustations forming during periods of high sea level.
These formations, along with a light-colored band on the submerged bridge, serve as proxies for precisely tracking historical sea-level changes and dating the bridge’s construction.
Previous research suggested human presence as far back as 9,000 years, but inconsistencies and poor preservation of the radiocarbon dated material, such as nearby bones and pottery, led to doubts about these findings.
Newer studies have used charcoal, ash and bones found on the island to create a timeline of human settlement about 4,400 years ago.
This aligns the timeline of human presence with significant environmental events, such as the extinction of the goat-antelope Myotragus balearicus.
By analyzing overgrowths of minerals on the bridge and the elevation of a coloration band on the bridge, the authors discovered the bridge was constructed nearly 6,000 years ago, more than 2,000 years older than the previous estimation — narrowing the timeline gap between eastern and western Mediterranean settlements.
“The history of the bridge construction appears to be closely associated with rapid Holocene sea-level rise just prior to 6,000 years ago and a brief sea-level stillstand that led to some upper sections of the cave being flooded,” they said.
“According to our chronology, the sea-level rise ceased and remained stable for several hundred years between 5,964 and 5,359 years ago. During this time, the so-called phreatic overgrowths on speleothems (POS) formed in the cave lake, and a distinctive ‘bathtub ring’ developed on the bridge.”
“The building of the bridge likely began early during this period, when crossing the 0.25 m-deep lake required its construction. However, the structure must have been completed before 5,600 years when the upper part of the bridge became submerged.”
“Evidence indicates that humans constructed a stone-paved pathway leading to the cave’s water pool and a robust bridge, facilitating access to the only other dry section of the cave situated beyond the lake, in the Sala d’Entrada.”
“The exact reasons behind the construction of these structures in Genovesa Cave remain elusive.”
“Nevertheless, the chronological constraints posed by the depth of the bridge, coupled with the similar depth at which POS and the coloration mark occur, support the idea of an early human presence on the island by 5,600 years ago and potentially dating back as far as 6,000 years ago.”
A paper describing the findings was published today in the journal Communications Earth & Environment.
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B.P. Onac et al. 2024. Submerged bridge constructed at least 5600 years ago indicates early human arrival in Mallorca, Spain. Commun Earth Environ 5, 457; doi: 10.1038/s43247-024-01584-4
