It’s long been known that Neolithic Orkney was in contact with distant places down the west coast of Scotland and on to Ireland, Brittany, Iberia and the Mediterranean. Megalithic stones and circles and chambers show this, and also archaeological finds such as types of stone or cattle bones from elsewhere. Last year geologists showed that the Altar Stone at Stonehenge has its origin somewhere in the Orcadian Basin, the region of ancient rock that stretches from the south of Shetland to the coast of Moray.

But how to transport a 6-tonne stone slab many hundreds of miles, from Scotland to Stonehenge? Dr Mark Cooper of the University of Washington is a biophysicist with a deep interest in archaeology and ancient ships. He describes possible forms of boat construction that would have been strong enough to cope with the Irish Sea and the North Sea, as well as the Pentland Firth – and also methods of navigation, and thus systems for measurement of length and time.

The story of the rocks of the Orcadian Basin can be found on the Orkney Landscapes website, and the work on the Altar Stone is described in a feature in The Conversation.