Deep in the forests of northern Burgundy, in a once disused quarry, a team of master-builders is building a 13th-century castle from scratch. Quarrymen, stonemasons, woodcutters, carpenter-joiners, blacksmiths, tile makers, carters and rope makers are working together to revive heritage craft skills and to shed light on the world of medieval construction.

“They work with the ethos that the surest way of re-discovering lost techniques and methods is by discovering first hand what works and what does not,” says the BBC, which made a program about the project called Secrets of the Castle. “Archaeologists and academics flock to the castle to see their theories tried out and put into practice. Above all, building a medieval castle requires the skill and co-operation of a workforce functioning together as a community.”

And this amazing project turns out to have an extremely useful part to play in a huge 21st century project – the restoration of Notre Dame Cathedral, in Paris.