Image copyright National Museum Wales Image caption An artist's impression shows how the Llys Rhosyr settlement might have looked

Work to reconstruct one of the medieval courts of the Princes of Gwynedd has begun at St Fagans National History Museum, near Cardiff.

Rebuilding the great hall from Llys Rhosyr on Anglesey will be one of the most challenging archaeological projects in Wales, said the museum.

It will see the building's nine-metre high (29.5 ft) stone walls and thatched roof rebuilt.

It is part of wider renovations of St Fagans.

Once complete, schools and groups will be able to stay overnight.

What was Llys Rhosyr?

Image copyright Rhion Pritchard Image caption Llywelyn Fawr was the most powerful of the Welsh princes in the early 1200s

Llys Rhosyr was one of the royal courts of Llywelyn Fawr - Llywelyn The Great (1172-1240) - who was prince of Gwynedd in the 13th Century, succeeded by his son Dafydd ap Llywelyn

The princes ruled by touring their realm and sitting in courts in small administrative areas called "commotes". Each had a Llys (court)

Llys Rhosyr was at the heart of the Menai commote near where Newborough parish church is now

King Edward I's conquest of 1282 led to Rhosyr being largely abandoned

Around 1330 a sandstorm buried the site beneath sand dunes

It was discovered in 1992 by archaeologist Neil Johnstone

The site was partially excavated, including a large main hall and a building thought to have housed the prince's private rooms

The reconstruction at St Fagans will be a re-imagining of what the great hall would have looked like

Sources: Friends of Llys Rhosyr and St Fagans National History Museum

The redevelopment, funded by the Heritage Lottery Fund and the Welsh government, includes a new building to illustrate the story of Wales from 230,000 BC and an Iron Age settlement Bryn Eryr, also from Anglesey.

The revamp has provided two apprenticeships with the museum's historic buildings unit.

Trainee stonemasons Matthew Roberts and Brett Burnell will join the team after funding was granted by the People's Postcode Lottery.