Scientists appear to be close to solving the mystery of how the 31 pyramids, including the world-famous Giza, were built in Egypt more than 4,000 years ago.

A research team from the University of North Carolina Wilmington discovered that the pyramids were likely built along a lost, ancient branch of the Nile River, which today lies hidden beneath desert and farmland.

For many years, archaeologists believed that the ancient Egyptians must have used a nearby waterway to transport materials such as the stones needed to build the pyramids across the river.

However, until today, “no one was sure of the location, shape, size or proximity of this great waterway to the actual site of the pyramids,” according to one of the study’s authors, Professor Eman Ghoneim.

In a cross-continental effort, the team of researchers used satellite radar images, historical maps, geophysical surveys and sediment coring, a technique archaeologists use to recover evidence from samples, to map the branch of the river they believe was buried by great drought and sandstorms thousands of years ago.

The team was able to “penetrate the surface of the sand and produce images of hidden features” using radar technology, according to the study, published in the journal Nature. Among those features were “buried rivers and ancient structures” that run along the foothills where “the vast majority of ancient Egyptian pyramids are located,” Professor Ghoneim said.

Speaking to the BBC, one of the study’s co-authors, Dr Suzanne Onstine, said “by identifying the actual branch of the river and having the data to show that there was a waterway that could have been used to transport heavier loads, equipment and of humans really help us explain pyramid construction.’

The team found that the branch of the river, called the Ahramat branch, a name that means pyramids in Arabic, was about 64 km long and between 200-700 meters wide. The branch of the river was bordered by 31 pyramids, which were built between 4,700 and 3,700 years ago.

The discovery of this extinct branch of the river helps explain the high density of pyramids between Giza and List, a Middle Kingdom burial site, in an inhospitable region of the Sahara desert. The proximity of the river branch to the pyramid complexes suggests that it was “active and functional during the construction phase of these pyramids,” the research says.

Dr Onstine explained that the ancient Egyptians could “use the power of the river to move these heavy blocks, instead of human labour”, adding, “it required much less effort”.

The Nile River was the lifeline of Ancient Egypt – and remains so to this day.