Ice Age Refuge Beneath a Serbian Fortress Reveals How Stone Age Humans Survived the Deep Freeze

Beneath the foundations of the City Museum of Novi Sad, inside one of Serbia’s most famous landmarks, a thin blanket of dusty sediment has been quietly preserving a secret from the depths of the last ice age. A team of geoarchaeologists and quaternary scientists led by Slobodan B. Marković and Zoran M. Perić has now decoded that layer, and their findings, published in the E&G Quaternary Science Journal, suggest that the slopes of Petrovaradin Fortress were far more than a convenient campsite for Stone Age hunters. During the coldest and driest millennia of the Late Pleistocene, the northern foothills of Fruška Gora Mountain appear to have functioned as a biological and human refuge, a patchwork of steppe, woodland, and wetland habitats where both animals and Gravettian people could weather one of the harshest climatic episodes in recent Earth history.

The story begins with an excavation that is unusual even by the standards of urban archaeology. Three phases of investigation have taken place around the museum building at Petrovaradin Fortress, the baroque stronghold that towers over the Danube at Novi Sad. The most recent campaign, carried out in 2022 inside the southern part of the museum itself, covered a modest 27 square metres. From that small footprint the researchers extracted two loessic sections, labelled PT1 and PT2, each roughly 60 centimetres thick. Loess, the wind-blown silt that blankets much of the Carpathian Basin, is one of the most valuable terrestrial archives of ice age climate, and even a half-metre of it can encode thousands of years of environmental change. In these sectors, the excavators also recovered artefacts from the Upper Palaeolithic, specifically the Gravettian technocomplex, linking the sediment record directly to the people who once lived there.

To squeeze every drop of information from such a compact sequence, the team deployed a battery of complementary techniques. Samples collected at 2.5-centimetre intervals were analysed for magnetic susceptibility, a proxy that tracks the concentration of fine magnetic minerals and often signals periods of soil formation and warmer, wetter conditions. Colour measurements taken with a Konica Minolta Chroma Meter recorded the lightness and chromaticity of the sediment in the CIE Lab* colour space, allowing the researchers to distinguish between dark, organic-rich palaeosol horizons and pale, unweathered loess. A handheld Thermo Scientific NITON XRF analyser provided the concentrations of seven elements, from which the team calculated the Rb/Sr and Zr/Sr ratios that serve as standard indices of chemical weathering and pedogenesis. Finally, 10-kilogram bulk samples were washed through sieves to recover fossil land snail shells, the unsung heroes of ice age palaeoecology.

The lithostratigraphy of the two profiles revealed three distinct units. Unit I, the uppermost layer, consists of homogeneous pale-brown silt studded with black spots of organic matter trapped in former root pores, resembling a weakly developed initial mollic horizon. Unit II is a transitional zone containing dispersed pebbles, small carbonate concretions, and angular blocks. Unit III, the basal layer, is a poorly sorted sandy coarse silt with carbonate concretions, root fissures, and thin, weakly developed soil horizons, capped by a discontinuous pebble layer at its base. These units correspond closely to the three uppermost stratigraphic units identified during earlier excavations at the site in 2011, and their magnetic susceptibility patterns rise steadily from values of around 24 to 33 SI in Unit I towards 40 SI in Unit III, mirroring records from nearby loess profiles.

The chronological anchor came from a single fragment of charcoal recovered at a depth of 45 centimetres in profile PT1. Radiocarbon dating at the A.E. Lalonde AMS Laboratory in Ottawa produced a conventional age of 23,895 plus or minus 77 radiocarbon years before present. Calibrated against the IntCal20 curve using OxCal v4.4, the date spans 28,272 to 27,773 calibrated years before present at 95.4 percent probability. That places the fire event, whether natural or human-made, squarely in the run-up to the Last Glacial Maximum, and supports the interpretation that the sequence accumulated during Marine Isotope Stage 2 and possibly the youngest part of MIS 3. In other words, the sediments record the very interval when Gravettian populations were concentrated in the southern Pannonian Basin before the deepest cold of the glacial peak.

The mollusc assemblages turned out to be the most revealing archive of all. Profile PT1 yielded 167 shells representing seven species, while PT2 produced a remarkable 466 shells across 12 species and 11 genera, with individual samples containing up to 12 species and 119 shells. Species richness and abundance increased towards the top of both profiles. Among the identified taxa were Pupilla triplicata, Vallonia costata, Granaria frumentum, Clausilia dubia, Chondrula tridens, and Punctum pygmaeum, alongside Vitrea crystallina, the only species present in every sample, which today inhabits riparian woodlands, humid meadows, and swampy environments. Crucially, PT2 also contained rare cold-adapted species such as Columella columella, Vertigo geyeri, and Vallonia tenuilabris, frigophilous indicators of the Last Glacial Maximum that are seldom found in Serbian loess sequences.

Reading these assemblages through the ecological classification frameworks of Ložek and Sümegi and Krolopp, the researchers reconstructed a landscape of striking heterogeneity. More than 40 percent of many samples consisted of species that prefer moderate conditions or display high ecological plasticity, while PT2 additionally hosted cold-resistant and sub-hygrophilous taxa absent from PT1. The two profiles, separated by only a short distance, therefore recorded subtly different environments: PT1 dominated by open grassland species, PT2 reflecting a more humid setting with forest-dwelling elements. Together they point to a mosaic of parkland vegetation, a shifting patchwork of wooded pockets, dry grassland, and moist hollows that gradually gave way to more open steppe as the Late Pleniglacial progressed. Such fine-grained environmental diversity over small spatial scales, the authors argue, may have been a decisive factor in sustaining long-term human occupation in the region.

The broader climatic picture that emerges is one of relative stability. Compared with loess regions of western and central Europe, where the same period witnessed pronounced environmental oscillations, the southeastern Carpathian Basin appears to have experienced comparatively minor variability. Weathering indices from PT1 and PT2 match the weakly weathered Late Pleniglacial loess of the nearby Mišeluk 2 sequence and the Batajnica loess-palaeosol sequence, confirming that soil formation was minimal throughout. Yet the molluscs indicate that conditions here were more humid than elsewhere in the southeastern basin, and the continuous presence of shells through the glacial sequence, where interglacial palaeosols in the region are typically sterile, confirms a glacial origin for the deposits. The northern slopes of Fruška Gora, the team concludes, likely acted as a biogeographical island and glacial refugium where forest elements persisted even at the height of the ice age.

Geography reinforced ecology. The Petrovaradin rock formation, perched on a Danube terrace at the junction of mountain, river terrace, and alluvial plain, offered sweeping visibility over the surrounding terrain, an obvious advantage for monitoring game and organising hunts. During the Pleistocene the landscape was gentler than today’s steep cliff: the Danube then flowed further north, and the slopes between the rock and the river were less abrupt, an open terrain comparable to settings occupied by Palaeolithic humans in northern Greece during the same period. Nearby deposits of white flint, extensively exploited during the Middle and Upper Palaeolithic, added a raw-material incentive for repeated visits. The Upper Palaeolithic lithic assemblages from the site correspond to the technologically impoverished industries typical of the Late Gravettian and Early Epigravettian, consistent with the idea that Gravettian groups clustered in the southern Pannonian Basin before the Last Glacial Maximum.

What makes the Petrovaradin study compelling is the way it stitches together so many strands, sedimentology, magnetism, colour, geochemistry, radiocarbon dating, and fossil snails, into a single narrative of survival. A half-metre of dust beneath a museum floor has shown that an ice age landscape was not a uniform wasteland but a living mosaic, and that its mosaic quality may have been precisely what drew people back, generation after generation, to the same strategic hillside above the Danube. The authors recommend that future excavations at archaeological sites sample multiple profiles to capture the full environmental range that Palaeolithic communities encountered, and they call for more detailed malacological work to fully understand the Fruška Gora refugium. For now, the fortress that guarded the Danube in the eighteenth century has revealed that it was guarding something far older: a pocket of habitable world in a frozen continent.

Subject of Research: Palaeoenvironmental reconstruction of the last glacial loess sequence at the Petrovaradin Fortress Palaeolithic site in Serbia

Article Title: Environmental reconstruction of the younger loess sequences of the Petrovaradin Fortress Palaeolithic site (Novi Sad, Serbia)

Article References: Marković, S. B., Mihailović, D., Bosnić, M. G., Krsmanović, P., Hughes, P. D., Pilipović, A., Roksandić, M., Hao, Q., Wang, L., Kolundžija, J., Puhar, D., Marković, R. S., Lukić, T., & Perić, Z. M. (2026). Environmental reconstruction of the younger loess sequences of the Petrovaradin Fortress Palaeolithic site (Novi Sad, Serbia). E&G Quaternary Science Journal, 75(1), 73-84. https://doi.org/10.5194/egqsj-75-73-2026

Image Credits: AI Generated

DOI: 10.5194/egqsj-75-73-2026

Keywords: loess, Petrovaradin Fortress, Palaeolithic, Gravettian, Last Glacial Maximum, molluscs, geoarchaeology, Serbia, Carpathian Basin, Marine Isotope Stage 2, refugium, Fruška Gora