TREIGNY, France (Reuters) - Blacksmiths, stonemasons and quarrymen are hard at work in a Burgundy forest building a 13th century-style castle using the most basic tools and materials, replicating the methods used hundreds of years ago to better understand them.

Forgoing all modern technology, workers use hammers to break stones and forge iron, operate wooden wheels to hoist their materials up to where they are needed, and rely on a quarry for stone, clay and sand as they build up a castle from scratch.

Construction on Guedelon Castle in central-eastern France began in 1997 after an archaeological survey revealed a medieval fortress hidden inside the walls of nearby Chateau de Saint-Fargeau.

Those behind the project hope to answer questions about medieval construction and provide lessons on sustainable building.

Around 40 people work at the site.

“The point of what we’re going to do here is...also help better restore ancient heritage,” 44-year-old stonemason Clement Guerard, who has worked on the site since 1999, told Reuters.

“What is perhaps frustrating is that what we do takes a lot of time. In the modern world, we are used to working very quickly... Here, we want to focus on quality more than quantity, and you have to forget some of the pace of modern life to be able to adapt to working by hand.”

After initially being funded, the project is now financed by the roughly 300,000 tourists who visit each year to see the castle slowly come together. Hundreds of people also come each year to work on the project.

This year, the masons are working on parts such as the western corner tower, the western curtain wall and chapel tower.

“I don’t like using electric tools, except perhaps drills, so when I came here, I found the use of hand tools was natural,” said retired Briton Nick Platt, who is spending two weeks at the site to improve his building skills.

“But the saws that we use are very, very different and initially quite cumbersome to use. But now I find they are eminently perfect for the job.”

As it takes time for people to adapt to the ancient building methods, Guedelon is being built at half the pace that medieval castles typically took, with those behind the project anticipating at least a further 10 to 15 years of construction. They also hope to expand by building a medieval village in future.

“It’s hard to imagine that in the Middle Ages it could come about like that,” tourist Nathalie Bonis said.

“It allows future generations to imagine what our ancestors were able to do.”