The mystery of the Preseli bluestones is unravelled tonight (Tuesday) in BBC Four's Hidden Histories.

The five-part series, broadcast at 7.30pm, follows the everyday investigative work of the Aberystwyth-based Royal Commission on the Ancient and Historical Monuments of Wales.

Tonight's episode explores the link between Stonehenge and the magical bluestones of west Wales.

It is claimed the bluestones originated in Pembrokeshire's Preseli hills, an area rich in remains like the 5,500 year old Neolithic burial chamber at Pentre Ifan.

Until relatively recently, little work had been done to establish where the stones came from or why, although several conflicting theories exist.

In this evening's programme, leading archaeologists and commission staff discover more evidence about their origin and identify one of the earliest settlements in the UK nearby.

Tonight's programme also explores how Swansea changed from a medieval town to a modern city after the World War Two bombing raids, seen through the commission’s aerofilms collection of historic aerial photos.

The first episode also looks at how nature has reclaimed the highest house in Wales; the ghostly ruin at Gwylfa Hiraethog, a decaying mansion on the Denbigh Moors.

“Hidden Histories is a fantastic series and it has been great to see the positive response in Wales to these new programmes," said Dr Peter Wakelin, secretary of the Royal Commission.

"It shows how much interest there is out there and the variety of wonderful heritage we have in our small nation. I hope, with this transmission throughout the UK on BBC Four, that a wider audience will be able to appreciate the amazing history that exists all around us.”