[Narrator:] Could the Celts and Carthaginians have made it as far as Kuelap... the giant fortress built by the Chachapoya in the mountains at 10,000 feet?

This computer reconstruction reveals that in terms of the massive stone used, Kuelap is even bigger than the Cheops pyramid in Egypt.

The Chachapoya were fantastic masons.

But where did they obtain the knowledge to build structures like this?

For over 25 years, archeologist Warren Church of Columbus State University has studied the Chachapoya.

He does not see the Celtic- Carthaginian influence in the ruins of Kuelap, as Giffhorn does.

He sees the heritage of a powerful Andean culture.

- They're really best known for their architecture.

But that is what we see now.

That's the best preserved thing that sits on the surface, as we as visitors walk around.

And some its really quite spectacular.

Some of it is monumental.

It speaks power.

- [Narrator:] Peter Lerche has been living in Peru for more than 30 years.

He was even mayor of the provincial capital.

He is completely captivated by the people here -- the living and the dead.

- How can we explain Kuelap?

All the C-14 analyses weve performed so far suggest that it's not really very old.

It dates from around 800 A.D.

The exception is here, the main entrance -- 500 A.D.

The first time I encountered Kuelap, I was particularly puzzled because no other fortress in the whole of America displays similar construction techniques.

But I knew fortresses like this were quite common in the Mediterranean region during classical times.

- [Narrator:] One detail in the main temple at Kuelap appears to support Giffhorns's theory.

The head engraved in the wall is reminiscent of a gruesome practice on the other side of the Atlantic.

The Celts would decapitate their prisoners, and hang their heads as a proud demonstration of power.

Did the Chachapoya also practice this ritual?

The Celtic custom of using human heads as trophies is connected with their belief that the soul resides in the skull.

That's why they treated the head as hugely important.

And this also explains why they were masters of trepanation.

But they weren't the only ones!