- [Narrator] Most visitors come all the way to Easter Island because of these stone statues, the moai.

Constructed between 1300 and sometime after the 1700s, there are more than 1000 of these giant carved figures scattered across the landscape.

Cut from volcanic rock, some are more than 30 feet high.

Over time, all of the moai have fallen down.

The 50 or so that are upright today were put back up in recent decades.

With their backs to the sea, they stare in passively into the island, arms held rigidly by their sides.

Some stand on ceremonial platforms known as ahu.

Others are sunk into the earth.

How could the Rapa Nui build and transport the moai?

When Carl and Terry analyzed the moai lying by the roads that led from the quarry, they noticed something significant.

A moai on the ahu has a flat base, so the statue stands straight up.

But most of the moai lying on the road have angled bases, and Carl and Terry believe that angle had a very specific purpose.

- Road moai has to be shaped in a way that can be transported.

They did it by shaping their base, so they leaned forward to enable them to walk.

This is a great example of the forward lean of these transport moai.

If you took this statue and we could put it back up, it would be leaning really far forward.

It means that as you rock it side to side, it falls forward across that front edge and takes a step.

Without that, it would just rock back and forth and not really go anywhere.

- [Terry] And walking really describes what these moai did.

- [Narrator] To test their theory, in 2012, Carl and Terry built a model of a moai out of concrete, carefully mixed to match the fragile density of the ancient statues volcanic rock, and made it walk.

- In our experiment, we found it took remarkably few people to move the statue, and we were terrible at it, you know?

We were the least expert of any people who've ever moved a moai in the world, but we were able to do a five ton statue with 18 people.