We found hundreds of huge ancient mass graves hidden in the Sahara desert

LYON: We have been on a years-long campaign of satellite remote sensing of the vast desert landscapes in Eastern Sudan.

This involved using satellite aerial imagery to systematically and painstakingly search for archaeological features in Atbai Desert of Eastern Sudan, a small part of the much larger Sahara.

Our team, which includes archaeologists from Macquarie University, France's HiSoMA research unit, and the Polish Academy of Sciences, wanted to tell the story of this desert region between the Nile and the Red Sea, without having to excavate.

One mysterious archaeological feature stood out. We kept finding large, circular mass graves filled with the bones of people and animals, often carefully arranged around a key person at the centre.

Likely built around the fourth and third millennia BCE, all these "enclosure burial" monuments have a large round enclosure wall, some up to 80 metres in diameter, with humans and their cattle, sheep and goats buried inside.

Our new research, published in the journal African Archaeological Review, reveals how we found 260 previously unknown enclosure burials east of the Nile River, across almost 1,000km of desert.

Who built them?

Already known from a few excavated examples in the Egyptian and Sudanese deserts, these large circular burial monuments have long puzzled scholars.

What seemed once isolated examples emerge now as a consistent pattern. It is suggestive of a common nomadic culture stretching across a vast stretch of desert.

Most are within the borders of modern Sudan on the slopes of the Red Sea Hills. Unfortunately, satellite imagery alone cannot communicate the whole story of these enclosure burial builders.

The carbon dates and pottery from the few excavated monuments tell us these people lived roughly 4000-3000 BCE, just before Egyptians formed a territorial kingdom we know of as Pharaonic Egypt.

But these "enclosure burial" nomads had little to do with urbane and farming Egyptians.

Living in the desert and raising herds, these were Saharan desert nomads through and through.

A new elite?

Some enclosures show "secondary" burials arranged around a "primary" burial of a person at the centre, perhaps a chief or other important member of the community.

For archaeologists, this is important data for discerning class and hierarchy in prehistoric societies.

The question of when Saharan nomads became less egalitarian has plagued archaeologists for decades, but most agree it was around this time of the fourth millennium BCE that a distinctive "elite" class emerged.

This is still a far cry from the sort of huge divisions between ruler and ruled as seen in societies such as Egypt, with its pharaohs and farmers. However, it ushers in the first traces of inequality.

Animals held in high esteem

Cattle seem very important to these prehistoric nomads (a theory also supported by ancient local rock art in the area).

Burying themselves alongside their herd, these nomads show they held their animals in esteem.

Thousands of years later, local nomads chose to reuse these now "ancient" enclosures for their burial plots, sometimes almost 4,000 years after they were first built.

In other words, the prehistoric nomads created cemetery spaces that lasted for millennia.

What happened to these people?

No one can say for sure.

The few dates we have for these monuments cluster between 4000-3000 BCE, nearing the end of a period when the once-greener Sahara was drying, a phase scientists call the "African Humid Period".

From north to south, the summer monsoon gradually retreated, reducing rainfall and shrinking pastures. This led nomads to abandon thirsty cattle, increase the mobility of their herds, migrate to the south or flee to the Nile.

The monuments are overwhelmingly located near what were then favourable watering spots; near rocky pools in valley floors, lakebeds and ephemeral rivers.

This tells us that when the monuments were being built, the desert was already quite challenging and dry.

At some point, as grass and bush made way for sand and rocks, keeping their prized cattle became unsustainable.

Having large herds of cattle in this desert, at this period, may have been a way of showing off an expensive and rare possession, a prehistoric nomad's equivalent to having a Ferrari. This may help explain why cattle were frequently buried alongside their owners in enclosure burial monuments.

A bigger story

These enclosure burials are only one part of the greater story of human adaptation to climate change across North Africa.

From the Central Sahara, to Kenya and Arabia, keeping cattle, goats and sheep transformed societies. It changed the food they ate, the way they moved around, and community hierarchies.

It's no coincidence communities changed how they buried their dead at the same time as they adopted herding lifestyles.

These burial enclosures tell us even scattered nomads were extremely well-organised people, and expert adapters.

Our discovery reshapes the story of the Sahara deserts and the prehistory of the Nile.

They provide a prologue for the monumentalism of the kingdoms of Egypt and Nubia, and an image of this region as more than pharaohs, pyramids and temples.

Sadly, many of these enclosure monuments are currently being destroyed or vandalised as a result of unregulated mining in the region. These unique burials have survived for millennia, but can disappear in less than a week.