there's been a medieval castle under construction in France.

The builders and designers here are using plans and techniques

that are as historically accurate to the 13th century as possible.

Guédelon Castle is experimental archeology and a tourist attraction.

The techniques rediscovered here,

they're now helping with the reconstruction of Notre Dame Cathedral.

But I'm here for one very specific piece of technology

that I'd never heard of,

and which to me feels like something

out of the anachronistic fiction of Astérix or the Flintstones.

It's called the treadmill crane

and it is a real thing from history.

Now I'm not an archeologist or a historian

so I'm going to let someone tell you about this place, and about this crane,

while I actually go and get some stone

and learn to power this thing.

- So when we say we're building a medieval castle,

of course we have to be very clear

about which period of the Middle Ages we're interested in.

So we've narrowed down our area of interest

to the 13th century.

To be even more precise, when we laid the first stone

we said it was the year 1228

and each year we move forward in history.

So this year on site, you are in the year of our lord 1253.

So in order to find out what technology was available at that time,

we have a number of different sources.

We use illuminated manuscripts, stained glass windows, financial records.

Of course we work with archeologists, art historians, and castellologists.

And so we've got all that information together

in order to decide how the castle should be built.

Sometimes we know how to do it,

sometimes these skills have never been lost,

others have been completely lost

and we have to then revive them from scratch.

The castle itself will be finished in about another 10 years.

So we're taking about 35 years in all to finish the castle

which is a really long time compared to the Middle Ages.

Because one of the reasons that we're building this castle

is to show the visiting public.

So half the time my colleagues are putting down their tools

in order to explain the work we're doing.

- So here we are at the single drum winch.

- Okay. So that needs to go up there.

- Yes. - Okay.

- We can provide the tower with those rocks, so we can build it.

- Okay.

- We might say that we're building a 13th century castle

but in terms of health and safety we're clearly in the 21st century.

So you will see anachronisms on site.

We have hard hats,

steel toe capped shoes, protective eyewear,

masks when we're working with the sandstone from the quarry.

All the scaffolding is heavily reinforced.

So obviously we're not trying to discover

how many people were killed or injured in the 13th century.

- So take care of your back.

- The castle that we're building here today

is the castle that would've belonged

to a low ranking local fairly modest nobleman.

This isn't a royal castle.

It's essentially being built as a private home

but there will be defensive elements within the castle.

There'll be a portcullis,

there'll be murder holes, arrow loops, crenelated walling.

And all of this even though there's very little chance

that the castle would've been attacked in the middle of the 13th century

these features are still in place. You never know.

- There's not any fancy modern pulleys or anything like that, it's just--

- No no, it just--

- Diameter of this versus diameter of this.

- Yes. It's like if you were making a effort of five flights of stairs.

So if you are walking 10 meters, it's one meter up.

- It's like a giant gear, basically.

- So we have a couple of single drummed cranes

and we also have a double drummed tread wheel winch.

And the advantage of that particular piece of machinery

is that it pivots through 360°.

So that allows us to hoist loads up from the quarry

and then spin the machinery around

and place it exactly where we need it on the masonry.

With the double drum winch

we can hoist somewhere in the region of 500 kilos,

that's 1,000lb in weight.

With a single drum winch,

well, there's one person working so it's half,

250 kilos roughly.

- So I'm going to lift 200 kilos.

- With this one. - All right.

- 150, 200. - Okay.

- Safety is obviously paramount when we're using this machinery.

So we have someone who's responsible for applying the brakes.

It means that there's no danger

of spinning round like in a washing machine.

We have someone who's at the base, responsible for charging the cradle.

And then one person who is in charge of the whole operation

keeping an eye on how far the walkers still have to walk.

Because of course when you're in the machine

you can't necessarily see.

So it's a very carefully managed process.

This is a technology that goes back to Roman times

but which is being used in the 13th century in cathedral construction.

We know that they were in use

because there are a number of medieval cranes

that still exist in the roof timbers of cathedrals.

Canterbury Cathedral, for example, has a wonderful example of that.

- Are you going to be on the brake?

Does it have a brake? - Yes.

Look.

This is normal brake, you can see here.

- Yep, it's just friction on that, that...

- There's no evidence of a braking system on these medieval cranes.

For safety reasons we've included one, so that we can stop it if necessary.

Strictly speaking, if all is well, you just stop walking.

- Okay.

- Okay just go ahead and watch your head.

- All right.

And right now this won't move 'cause you're on the brake, so...

- You can look at fixed points, to help you.

- Yeah 'cause if I'm looking at this... - Yeah it will be Disneyland!

Are you ready? - Ready.

- Okay.

- Just walk? - Walk.

- Oh! Oh wow.

And look to the side.

If I look ahead... it gets really confusing.

Got to look that way, got to look that way.

Hey, but it's working! - Yeah, it's working.

- Oh you're right about that fixed point. - Yes.

- I looked forward for a bit and started getting dizzy.

I'm just walking up a steep hill.

There is some kind of feedback loop,

the faster I walk the faster it turns,

then the faster it pushes me back.

'Cause of course I'm moving more.

But then I risk bashing my head into the axle behind me.

- So these machines are absolutely necessary in the construction process.

We couldn't build the castle at the rate we are without them.

We hoist somewhere in the region of three metric tonnes every day.

- There we go.

- Okay. - Okay.

- And stop!

Congratulations for your first medieval crane!

- Thank you.

I didn't expect quite the tourist applause there,

thank you very much.

- Always.