The Absence of Altar Stone Fragments in the Aubrey Holes at Stonehenge: Statistical Rarity or Evidence of a Late Arrival?

 

The Aubrey Hole Excavations

The Question

Why are there no identifiable fragments of the Altar Stone (Stone 80, a micaceous Old Red Sandstone) in the material recovered from the Aubrey Holes, despite the presence of representatives from virtually all other major and minor bluestone lithological groups? Is this absence meaningful—potentially indicating that the Altar Stone arrived later in Stonehenge’s construction sequence—or is it simply a statistical oddity resulting from the stone’s overall extreme rarity in the debitage record?

This question is worth asking because the Aubrey Holes represent one of the earliest structural features at Stonehenge (c. 3000 BC), and their fills provide a key window into the initial phases of bluestone activity. Understanding the timing and integration of individual stones, especially outliers like the Altar Stone, helps refine models of the monument’s multi-stage development and the logistics of long-distance stone transport.

Background and Why the Question Arises

The Aubrey Holes (56 pits forming a circle inside the bank and ditch) were excavated primarily by William Hawley and R.S. Newall in the 1920s, with a re-excavation of Aubrey Hole 7 in 2008. They have long been central to debates about whether they originally held bluestones or wooden posts.

Two important papers by Rob Ixer, Richard Bevins, and colleagues provide detailed modern petrographic re-analysis of historic collections:

• “And the first shall be last: the Aubrey Holes and their stones” (Ixer & Bevins, Wiltshire Archaeological & Natural History Magazine 114, 2021) examines ~46 thin sections from the 1920s Aubrey Hole material (primarily Holes 1–22 and 30) plus 2008 AH7 samples.
• “William Cunnington’s 1884 Stonehenge lithologies revisited” (Ixer, Bevins, Pirrie, Power & Pearce, WANHM 119, 2026) re-examines 33 thin sections from Cunnington’s late 19th-century surface and small excavation collections, providing a “pristine” pre-20th-century baseline.

Both papers update older material into the modern Ixer/Bevins bluestone classification scheme and confirm a restricted suite of Welsh-derived lithologies with no exotic glacial erratics.

The Evidence: Comparative Lithology

Table 1: Presence of Key Lithological Groups

Lithology Group	Aubrey Holes (2021)	Cunnington (2026)	Notes
Dolerites (spotted/unspotted)	Yes	Yes (incl. orthostats 32, 49, 61a)	Common in both.
Rhyolite Group C (Craig Rhos-y-felin)	Yes (dominant)	Yes	Ubiquitous.
Andesite/Volcanic Group A	Yes	Yes (type material from Stone 32c)	Cunnington defines the group.
Dacite/Volcanic Group B (SH38)	Yes (limited)	Yes (incl. from SH38)	Rare but present.
Rhyolite/Dacite Group D	Yes (single sample)	Yes (S57)	Both affirm genuine bluestone status.
Rhyolite Group E (SH48)	Yes	No	Absent in earlier collection.
Lower Palaeozoic Sandstone	Yes	Yes	Consistent.
Altar Stone (ORS sandstone)	No	Yes (S45)	Explicit absence in Aubrey Holes.
Greensand (packing)	Yes	Yes	Packing material.
Sarsen	Yes (common)	Absent in thin sections	Local.

The Aubrey Holes collection is comprehensive for bluestone groups except the Altar Stone, which is explicitly noted as absent.

Altar Stone Samples in Museum Collections

Verified or highly probable Altar Stone fragments are exceptionally rare across all museum holdings, reinforcing the pattern of scarcity. Many older labelled pieces have been re-evaluated and rejected through modern petrography, pXRF, and automated mineralogy.

Key examples include:

• Salisbury Museum sample 2010K 240 (also referenced as Wilts 277): Collected directly from the underside of the Altar Stone in 1844 by Mr Browne of Amesbury. This is the primary reference “type” sample, used extensively in recent provenancing (Scottish Orcadian Basin origin) and thin-section studies.
• Hawley/Newall 1920s excavated pieces (e.g., MS1–MS3; held in National Museum of Wales and related collections): Small fragments from excavations near Stone 1 or associated contexts; some authenticated via matching mineralogy/chemistry.
• Darvill & Wainwright 2008 excavation fragments (e.g., SH08 Context 1 FN196): Three probable pieces from within the Stonehenge Circle, authenticated by pXRF and petrography.
• Cunnington collection S45 (Wiltshire/Salisbury Museums): One sample from surface finds or small excavations in the Bluestone Circle area, identified in the 2026 paper.

Overall, Altar Stone debitage consists of tiny, lightweight pieces. No large concentrations exist, and many historic “Altar Stone” labels in museums have been disproven as other sandstones or tuffs.

Refined Provenance and Transport (Clarke et al. 2026)

New detrital zircon analysis strengthens a source in mainland northeast Scotland (Caithness/Sarclet area provides the closest match). Glacial modelling (Late Devensian British-Irish Ice Sheet) shows possible transport to Dogger Bank (~400 km from Stonehenge), but not directly to Salisbury Plain. Dogger Bank was exposed until ~8–7 ka BP, millennia before the Altar Stone’s likely emplacement at Stonehenge.

Clarke et al. float the idea that the Altar Stone may have had a convoluted route: glacial transport to Dogger Bank followed by later human hauling to Stonehenge. However, this would require an early arrival (pre-dating Doggerland flooding) or yet another undocumented stop along the route. There is no supporting evidence in the debitage record (including the Aubrey Holes or other early contexts) for such an early presence of Altar Stone material at or near Stonehenge.

Discussion: Rarity vs. Late Arrival

The Altar Stone is anomalous: it is the largest “bluestone” (~6 tonnes), recumbent, sourced from north-east Scotland (hundreds of km further than the Welsh bluestones), and possesses distinctive baryte cement. Its position (under a fallen sarsen from the Great Trilithon) and potential misalignment with the main bluestone phase invite questions about its integration timing.

Arguments for statistical oddity:

• Altar Stone debitage is demonstrably rare across all contexts, including museum collections and excavations. Even substantial samples (such as the Aubrey Holes material) can easily miss it by chance.
• Cunnington’s surface-focused collection captured one example, but later excavated pit fills (with different taphonomic and sampling biases, including Newall’s preferences) did not. The museum record shows the same low frequency everywhere.
• No Altar Stone in most debitage assemblages; its scarcity is a consistent pattern, not unique to the Aubrey Holes.

Arguments for possible late arrival:

• The Aubrey Holes are among the earliest features (~3000 BC). If the Altar Stone arrived later (possibly during sarsen phase rearrangements, c. 2500 BC or after), its fragments would not be expected in primary early fills.
• Its Scottish source suggests a separate long-distance transport event, potentially distinct from the main Welsh bluestone group.
• Its unique size, form, and position support the idea that it was handled differently or introduced at a different stage.

Conclusion

The absence of Altar Stone fragments in the Aubrey Holes is not strongly diagnostic of a late arrival, primarily because of the stone’s documented extreme rarity in the overall debitage record and museum collections. It is most parsimoniously explained as a statistical oddity given sampling limitations and the low frequency of Altar Stone material site-wide.

However, when combined with its anomalous Scottish provenance, large size, recumbent position, and potential chronological misalignment with the main bluestone phase, a later arrival or separate handling (including no support for a convoluted Doggerland route) remains a plausible and elegant explanation. The two papers together reinforce that Stonehenge’s “foreign” stones represent a limited, human-transported suite without glacial erratics, while highlighting the value of continued petrographic re-analysis of historic collections.

References

• Ixer, R.A. & Bevins, R.E. (2021). “And the first shall be last: the Aubrey Holes and their stones.” Wiltshire Archaeological & Natural History Magazine 114, 1–17.
• Ixer, R., Bevins, R., Pirrie, D., Power, M. & Pearce, N.J.G. (2026). “William Cunnington’s 1884 Stonehenge lithologies revisited.” Wiltshire Archaeological & Natural History Magazine 119, 1–19.
• Clarke, A. J. I., Veness, R. L. J., Kirkland, C. L., Clark, C. D., Gandy, N., Emery, A. et al. (2026) From Highlands to Henge: Refining the Provenance and Transport Pathways of Stonehenge's Altar Stone. Journal of Quaternary Science, 1–8. https://doi.org/10.1002/jqs.70080
• Bevins, R.E. et al. (2020–2025). Various papers on Altar Stone provenancing (e.g., Journal of Archaeological Science: Reports).
• Cleal, R.M.J., Walker, K.E. & Montague, R. (1995). Stonehenge in its Landscape: Twentieth-Century Excavations. English Heritage.