From highlands to henge: refining the provenance and transport pathways of Stonehenge's Altar Stone

The Altar Stone, the 6000 kg central sandstone megalith at Stonehenge in southern England, is suggested to have originated from the Orcadian Basin in northeast Scotland, some 700 km away. However, its source location within this large basin remains unresolved and its mode of transport uncertain. Proposed mechanisms include Neolithic human transport via marine or overland routes or southward movement as a glacial erratic. Here, we combine sandstone provenance analysis with ice flow modelling to constrain potential sources and transport pathways. Ice sheet reconstructions show that southward transport vectors from northeast Scotland were highly localised, making precise source determination critical to evaluating glacial erratic transport plausibility. Candidate source areas farther south within the Orcadian Basin are more compatible with southward glacial dispersal, but show weaker correspondence with the detrital zircon age spectra that characterise the Altar Stone. By contrast, sandstones from Caithness on the mainland of northeast Scotland provide the closest match in zircon age structure; yet, modelled glacial transport from this region is predominantly towards the north‐east, with a localised south‐eastward pathway directed towards Dogger Bank. Glacial dispersal to Dogger Bank would reduce the anthropogenic transport distance required to Stonehenge from 700 km to 400 km. However, such a model raises an additional temporal problem, as Dogger Bank was inundated by post‐glacial sea‐level rise before the Altar Stone likely arrived at Stonehenge. Glacial transport may have provided an intermediate stage in the stone's journey, but alone cannot account for the final emplacement on Salisbury Plain. Even under a glacially assisted scenario, substantial anthropogenic transport would have remained necessary.