- [Narrator] It is one of the most extraordinary and baffling archeological finds of recent years.

(speaking foreign language) - [Quirino Translator] As we cleared away the top layers of soil, we began to see stones in a circular arrangement, then platforms and terraces began to appear.

That really surprised us.

It seemed extraordinary.

(harmonious music) - [Narrator] As the full structure emerged, their surprise grew.

Here was a massive pyramid as tall as a five story building constructed from clay, stone, and reed with a mysterious stone spiral built on its summit.

The carbon-14 dates were even more astonishing.

The pyramid was built over 5,000 years ago, even before the pyramids of Egypt and Mesopotamia, a time when archeologists had believed the Amazon was populated only by hunter gatherers.

Montegrande rewrites the history of complex societies on the continent.

For over a century, when archeologists wrote about cities in high civilization in South America, they focused on cultures like the Inca of the Andes or the Nazca of the Pacific Coast.

But here at Montegrande is clear evidence of a complex society and monumental architecture at least 3,000 years older than either the Inca or Nazca.

- If you compare the evidence for early architecture of monumental architecture, of planned domestication, we see a lot of things happening before here in this part of Peru in the Amazon, not in the coast and not even the mountains.

So I think it really brings, it highlights importance that the place that Amazonian and indigenous people had in the cultural history of this part of South America.

- [Narrator] The excavation of an almost identical but much smaller spiral pyramid in Ecuador revealed a tomb.

This makes Quirino think that Montegrande also is the tomb of a religious leader.

If he's right, it would give meaning to the mysterious spiral so carefully constructed on top of it.

(speaking foreign language) - [Quirino Translator] The spiral is one of the most tensioned symbols in the history of humanity.

It signifies the beginning and the end of life, the endless creation of one generation from the preceding one.

(continues speaking foreign language) - [Quirino Translator] I am sitting at the center of the spiral architecture and right beneath me in the spiral center would be the tomb of that high status individual.

We believe that he's seated in a fetal position and from the center of his head, the spiral expands out like the the axis mundi, the axis of the cosmos.

(continues speaking in foreign language) - [Quirino Translator] This also probably had important astronomical associations, as in most ancient societies who studied the night sky, the stars, and linked them to life on Earth.

(harmonious music)