The search for a second Altar Stone - Andrew Collins

 Collins, Andrew. (2024). The Stonehenge Altar Stone: Its Origins, Composition, and Function, And the Search for Its Lost Companion. 

The most enigmatic "foreign" stone at Stonehenge is its Altar Stone. Long thought to have been sourced from the Old Red Sandstone beds of South Wales, new studies have focused on its origin in the Orcadian Basin of northeastern Scotland, either in the Caithness region or in the Orkney Isles. Despite one paper (Bevins et al, 2024) providing compelling evidence that the Altar Stone does not exactly match the composition of Old Red Sandstone beds on the Orkney Mainland, those responsible for transporting the stone to Stonehenge were almost certainly its original builders, the Grooved Ware culture, who first emerged on Orkney during the Late Neolithic. We look at everything known about the Altar Stone and how its presence at Stonehenge might relate to its construction. We also go in search of its lost companion, and examine where both these huge monoliths might have stood within the monument, and how all this might relate to the monument's underlying geometry.