Background and recent excavations

While miniature art in the form of engraved plaques is abundant from the late fourth and third millennia BC in Iberia, comparable finds are rare in the north-west European Neolithic, characterised by a few prominent examples from Orkney and southern England (Lillios Reference Lillios2008; Thomas Reference Thomas2016; Jones & Díaz-Guardamino Reference Jones, Díaz-Guardamino, Jones and Díaz-Guardamino2019). However, substantial numbers of engraved stones, generally labelled ‘sun stones’ after the rayed images that characterise many of them, excavated from two locations on the Danish island of Bornholm in the Baltic Sea are expanding the north-west European record. Vasagård and Rispebjerg are the only two Neolithic enclosure sites identified on Bornholm (Figure 1). While causewayed enclosures are found only at Vasagård, both sites include extensive palisaded enclosures that can be dated to the penultimate phase of the Funnel Beaker culture on the island, the Vasagård phase, c. 2900–2800 BC (corresponding to the Store Valby phase or Middle Neolithic V in southern Scandinavia, Nielsen & Nielsen Reference Nielsen and Nielsen2022: 124–28). In 1995 engraved stones started to appear during excavations at Rispebjerg, where more than 20 such specimens have now been found (Kaul et al. Reference Kaul, Nielsen and Nielsen2002, Reference Kaul, Andresen and Thorsen2016). Fragments of similar engraved stone plaques also appeared in excavations at Vasagård between 2013 and 2018, which mainly focused on the ditches of the western causewayed enclosure. This article presents a fundamental classification of this rich and unique collection of Neolithic art and offers an interpretation of its function and a possible reason for its deposition during a cold climate event c. 2900 BC.

Figure 1.

Bornholm with the location of the two sites mentioned in the text (after Meesenburg Reference Meesenburg1972: 5).

Vasagård is situated on the lower-lying southern part of Bornholm, which is composed of a till plain with pre-Quaternary sediments dominated by sandstone, shale and unconsolidated or poorly consolidated sediments (Frei & Frei Reference Frei and Frei2013). As a so-called ‘double enclosure site’, Vasagård comprises two neighbouring late-fourth-millennium BC causewayed enclosures with opposite orientation, known as Vasagård East and West (Figure 2). The two enclosures have semi-circular double ditch circuits and are separated by the Læså river valley, which forms an abrupt vertical river cliff to the west that truncates Vasagård West. To the east, a steep slope rises to Vasagård East, located on a hill. Finds from the ditches suggest that both causewayed enclosures were established by people of the Funnel Beaker (Trichterbecher) culture in the Early Neolithic around 3400 BC. The stratigraphy and the finds clearly show long-term use of the enclosures as the ditches were recut and filled in during the succeeding Middle Neolithic phases, c. 3000–2900 BC, whereupon the ditches went out of use (Nielsen et al. Reference Nielsen, Nielsen and Thorsen2024). Following the last major backfilling of the causewayed enclosure ditches, a series of palisades were erected to enclose most of the site, both East and West, and a series of circular post-build structures (‘timber circles’) was constructed. These features are probably contemporary with each other and date to 2900 BC or shortly thereafter (Nielsen et al. Reference Nielsen, Nielsen and Thorsen2024).

Figure 2.

Survey map of Vasagård (basemap: lidar map from the Danish Geodata Agency; graphics by Michael S. Thorsen).

Context, date and material

A total of 614 crafted plaques and plaque fragments carrying a variety of decorative motifs were found during excavations at Vasagård West between 2013 and 2018. The vast majority derive from the ditches of the causewayed enclosure, though a few were found in postholes belonging to one of the timber circles and some come from a cultural layer deposited in a shallow depression just next to the causewayed enclosure.

In the ditches, the engraved stones are delimited to a specific recurring layer (Figure 3). The stratigraphy, comparable between ditches, indicates a sealing of the lower layers of the ditches by a stone pavement dated by pottery inclusions to c. 3000–2900 BC. Most engraved stones were found in the lower section of the darker infilling layer that sits on top of the pavement (layer 2). This infill is dated by ceramic typology to the local Vasagård phase of the late Funnel Beaker culture, c. 2900–2800 BC.

Figure 3.

Section of ditch XIV of the causewayed enclosure at Vasagård West. The upper layer (1) with settlement debris from Middle Neolithic V, c. 2900–2800 BC, has a lower, more find-rich part (2), where most of the engraved stones have been found. Beneath this a stone layer (3–4) seals the lower deposits (5–10), which date from the Early Neolithic II to the Middle Neolithic III (c. 3400–2900 BC). At the bottom, redeposited morainic subsoils (9–10) consisting of clayey sand and gravel (11), rest upon solid bedrock of Upper Ordovician shale (12). The brown shapes represent pottery (photograph and graphics by Michael S. Thorsen).

That the engraved stones belong to a brief horizon around 2900 BC is confirmed by finds from the postholes of a circular post-build structure in trench XXIV, which contained engraved stones, pottery, charcoal and the remains of a decorated daub that likewise showed sun motifs (Figure 4). The circle of eight postholes in trench XXIV is 8m in diameter, surrounding a flat (altar?) stone that measures 1.00 × 0.75m and rests on a layer of crushed granite. The structure is interpreted as a cult building that functioned for a short time, after which objects and fragments of ornamented daub were deposited in the empty postholes. Eight such circular structures have been documented at Vasagård, while at least 24 are known from Rispebjerg (Nielsen et al. Reference Nielsen, Nielsen, Thorsen, Nielsen, Nielsen, Hansen, Paulsen and Thorsen2014, 110, fig. 5). The pottery from the circular structure in trench XXIV at Vasagård comprises vessels from two pottery traditions, one reminiscent of the finely decorated pottery known from Scanian passage graves (Figure 4, no. 3; e.g. Bagge & Kaelas Reference Bagge and Kaelas1950: pls. VI & VII), and the other from the more simply decorated Vasagård style (Figure 4, no. 4). The presence of both pottery traditions indicates that the engraved stones were deposited at the transition to the Vasagård phase of the late Funnel Beaker culture. A date c. 2900 BC is further supported by four radiocarbon dates on charcoal from the postholes (Figure 5).

Figure 4.

The circular structure in trench XXIV at Vasagård West and the objects found in the postholes: engraved stones (1, 2 & 5), pottery (3 & 4) and decorated burnt daub (6 & 7) (3 & 4 drawn by Freerk Oldenburger; photographs by John Lee, The National Museum of Denmark & René Laursen, Bornholms Museum).

Figure 5.

Calibrated radiocarbon dates for the circular structure in trench XXIV (figure by authors).

The engraved stones are made of different materials. Some are made of the hard, black shale from the Upper Ordovician bedrock at Vasagård, and which in some places is found less than 1m below the surface of the topsoil. Softer types of shale with a content of clay and fine sand, some in the shape of water-rolled pebbles, are also used, as well as naturally shaped pebbles of hard, fine-grained rock. Despite a natural tendency to delaminate, shale was clearly the preferred material for producing engraved stones as around 95 per cent are made of some kind of shale. Thin pieces of quartz (n = 4) and flint (n = 1), chipped into circular shapes without decoration, are also found at Vasagård.

Ornamentation and typology

Around 70 per cent of the engraved stone pieces from Vasagård West are fragments of which many are less than a centimetre in size with incised ornamentation. The more complete plaques are a variety of uneven shapes and sizes. To establish any meaningful categorisation of this diverse material, only the ornamentation provides a point of departure. The fact that most of the engraved stones are fragmented does, of course, make categorisation of small individual pieces difficult, which has resulted in a substantial residual group, but the limited range of recurring motifs allows us to establish a general typology based on a visual, qualitative identification of motifs (Figure 6, Table 1).

Figure 6.

The engraved plaques divided into types. VAS 1567 has a double motif and is depicted from both sides (type 3d and type 4) (drawings by Bente Stensen Christensen).

Table 1.

The number of engraved stones and fragments divided by type, subtype and material (total: 388).

A total of 388 plaques and plaque fragments from Vasagård West can be assigned to six motif types. All types vary in the skill in which engravings were executed, from seemingly quick, rough sketches to more time-consuming, meticulous specimens. In addition to the defined motifs, an ornamental edge is present on more than 40 per cent of the incised plaques that have preserved rims. Predominantly, these ornaments consist of short, radial strokes, here referred to as simple rim ornaments. In a few instances, semicircles are used instead (cf. Figure 6: VAS 3770). A correlation between shape and motif was already apparent at the time of excavation, indicating a division in two main categories: circular plaques with sun motifs (type 1) and oval or sub-rectangular plaques with plant motifs (type 4). Type 2 and 3 plaques are more heterogeneous in shape.

The darkened sun

The stone plaques engraved with sun and plant motifs were produced and deposited at Vasagård during a short period of time around 2900 BC. More than 20 engraved stones have also been recovered from the nearby site of Rispebjerg (Kaul et al. Reference Kaul, Nielsen and Nielsen2002, Reference Kaul, Andresen and Thorsen2016). At no point before or after this period do engraved stones appear in the archaeological record of either site. The scale and chronological restriction of this depositional event suggests that it was triggered by an incident, or the culmination of incidents, equally large in scale and acute in scope. Given the imagery carved into the stones, such an incident could be a natural disaster or climatic events that affected crop yields or the visibility of the sun.

No major solar eclipses were observed on Bornholm between 3000 and 2000 BC (NASA 2021), and it is unlikely that the brief disappearance of the sun would have been sufficiently impactful to provoke the mass production and deposition of engraved stones. However, a period of severe cooling before and after 2900 BC is independently corroborated by multiple sources (Figure 10). Studies of varves (annual sedimentation layers) from lakes in the Eifel region in Germany indicate an extreme reduction in sunlight during two periods, 2927–2892 BC and 2877–2872 BC (Sirocko Reference Sirocko, Meller, Arz, Jung and Risch2015). The annual growth of tree rings in sub-fossil wood from the Main Valley, also in Germany, reveals wood-anatomical markers indicating spring and summer frost events for four years between 2932 and 2929 BC, and for five years between 2885 and 2880 BC (Land Reference Land2014; Land et al. Reference Land, Schönbein, Friedrich, Meller, Arz, Jung and Risch2015). Other observations confirm that cooling events occurred several times around 2900 BC and affected the wider northern hemisphere. In the western USA, tree rings of bristlecone pine, notoriously long-lived species, show width minima at 2951, 2911, 2906 and 2905 BC. Furthermore, a frost marker is detected in the rings corresponding to 2906 BC. Allowing a plus-or-minus five-year deviation, the four years with tree-ring minima widths correlate with years containing sulphate in the GISP2 Greenlandic ice core—an inclusion that signals volcanic eruptions (Salzer & Hughes Reference Salzer and Hughes2007: tab. 2).

Figure 10.

Synchronisation of archaeological and climatic events close to 2900 BC (graphics by Mads Lou Bendtsen, The National Museum of Denmark).

Volcanic eruptions inject sulphate aerosols into the stratosphere. This creates a haze, which reflects solar radiation back into space. Hence, the increase of sulphate aerosols impacts climate and causes global cooling. It is therefore notable that a major volcanic eruption has been identified at 2931 ± 11 BC in Greenlandic ice cores (Vinther et al. Reference Vinther2006) and at 2910 ± 19 BC in ice cores in Antarctica (Cole-Dai et al. Reference Cole-Dai2021). The Greenlandic and Antarctic ice cores are synchronised, but follow different, absolute time scales: GICC05 and WD2014, respectively (Vinther et al. Reference Vinther2006; Sigl et al. Reference Sigl2016; see Sigl et al. Reference Sigl, Toohey, McConnell, Cole-Dai and Severi2022 for discussion). Nevertheless, there is an overlap between the uncertainty estimates of the two dates of the volcanic event as indicated in Figure 10. Furthermore, these dates correspond with the frost events identified in tree rings and the extreme reduction in sunlight detected in lake varves. A connection between volcanic eruption and frost markers in tree rings is also observed in AD 1912/13, when the Novarupta-Katmai eruption in Alaska (June 1912) caused spring frosts in 1913 that are recorded as wood-anatomical markers in oak tree rings for that year (Land Reference Land2014). The Novarupta-Katmai eruption is ranked as the largest of the twentieth century (volcanic eruption index six).

The c. 2910 BC volcanic eruption is likely to have affected weather and harvest across the northern hemisphere. The eruption of Mount Tambora in Indonesia in AD 1815 released enough ash and aerosols into the atmosphere to substantially inhibit sunlight and reduce global temperatures by nearly 3°C, precipitating crop failures across the world in the following year (Wood Reference Wood2015). On a list of the most powerful eruptions of the Holocene, the 2910 BC eruption is ranked as number 15 and the AD 1815 Tambora eruption ranks as number 26 (Sigl et al. Reference Sigl, Toohey, McConnell, Cole-Dai and Severi2022). Estimations suggest that the magnitude of the 2910 BC eruption was comparable to the Okmok II volcanic eruption in Alaska in 43 BC, also known as ‘the Caesar volcano’ mentioned by Plutarch and Pliny the Elder (McConnell et al. Reference McConnell2020). This eruption resulted in unusually cold, inclement weather, crop failures, famine and disease in the Mediterranean for more than two years.

We can assume, therefore, that a cooling event comparable to the one caused by the 43 BC eruption took place a few years before or after 2900 BC and coincided with the ritual deposition of the engraved stones. It is possible that this 2900 BC cooling event also had wider economic and social consequences for the people living in southern Scandinavia at the time, as it coincides with the beginning of the final Funnel Beaker phase. This phase is characterised by substantial changes in material culture, a break with the classic Funnel Beaker tradition, the cessation of megalithic tomb building and the formation of new networks and influences from the marine oriented Scandinavian Pitted Ware culture, which also affected Bornholm (Iversen Reference Iversen2010, Reference Iversen2020; Brozio et al. Reference Brozio, Filipović, Kirleis, Müller and Schmölcke2019; Nielsen & Nielsen Reference Nielsen and Nielsen2022: 141). Population decline, plague and widespread reforestation also indicate a general ‘Neolithic decline’ around this time (Allentoft et al. Reference Allentoft2024a and references therein; Seersholm et al. Reference Seersholm2024). This was followed by profound cultural and populational change as Corded Ware societies appeared with the influx of people from the Steppe north of the Black Sea into eastern, central and northern Europe. These events also affected Bornholm as we see the appearance of the Swedish-Norwegian Battle Axe culture from c. 2600 BC (Nielsen & Nielsen Reference Nielsen and Nielsen2022: 150–57; Allentoft et al. Reference Allentoft2024b). The turbulence of this period renders the long-lasting impacts of the 2900 BC cooling event on Neolithic societies difficult to isolate even if sporadic sun images on contemporary pottery and clay discs (cf. Kaul et al. Reference Kaul, Andresen and Thorsen2016: 29–32; Iversen et al. Reference Iversen, Becker and Bristow2024) might reflect this event. Furthermore, the crisis might have increased competition and conflicts, which could have encouraged the construction of palisade enclosures to defend special sites, where congregations and sacred rituals took place—not only on Bornholm but also elsewhere in southern Scandinavia where palisade enclosures were constructed (Brink Reference Brink, Furholt, Hinz, Mischka, Noble and Olausson2014). Yet at Vasagård and Rispebjerg we see evidence of a community gathering in a joint effort to enact change, engaging in the use of symbolism that was arguably directed toward the banishment of the darkened sun and the restoration of the harvest.