The Stonehenge Altar Stone was probably not sourced from the Old Red Sandstone of the Anglo-Welsh Basin: Time to broaden our geographic and stratigraphic horizons?

•Some have considered the Stonehenge Altar Stone to belong to the bluestone megalith grouping.•Historically, it has been thought to come from Wales, along with the other bluestones.•More detailed analysis has failed to find a source in Wales or adjacent areas.•We question the validity of ‘lumping’ the Altar Stone with the Welsh bluestones.•We intend to broaden our search for the Altar Stone source into northern Britain.