Stonehenge: Secrets Of The New Stone | Preview (5)

Actor Jason Watkins and Historian Tracy Borman investigate the final mystery of Stonehenge - the secret of the altar stone.

The altar stone is a six tonne slab at the very heart of Stonehenge, that has puzzled archaeologists for centuries. It’s the only stone that lies flat on its side, a different type from all the others, and the only stone whose origins are still unknown. Discovering where this huge stone came from could well be the key to understanding exactly why Stonehenge was built.

Since the 1920s, archaeologists have believed the altar stone came from Wales, along with the Stonehenge bluestones. In a TV first, Tracy and Jason uncover new research from Aberystwyth University that overturns this long-held theory. Scientists have found out that it came from far further afield than anyone imagined - somewhere in the northernmost reaches of Scotland.

This breakthrough sends Jason and Tracy on a journey to the very extremes of Britain, over land and sea, in search of more answers. They investigate why this curious stone was brought to Stonehenge, and the crucial role it may have played in solstice celebrations.

They try their hand at ancient techniques by which this six-tonne slab could have been transported around 500 miles by Stone Age people. And they learn more about the surprisingly sophisticated Neolithic communities who built the iconic stone circle.

Their travels take them all the way from Wiltshire to Orkney, where they explore some of the best-preserved Neolithic sites in the world - the vast Ring of Brodgar, and the incredibly intact Stone Age village of Skara Brae.

The pair’s journey reveals much more than the altar stone’s possible origins – it offers fascinating insight into how Stone Age communities across Britain were connected, and how Stonehenge itself may have been built as a way to celebrate the unification of Stone Age people across the country.

Stonehenge: Secrets Of The New Stone airs Tuesday 5th March at 9pm on 5.