Scientists may have solved the mystery of how the ancient Egyptians hauled millions of 2-ton blocks of stone through the desert to build the pyramids

• Ancient Egyptians built the spectacular Giza pyramids in what is now a desert landscape.
• How they hauled the tons-heavy building blocks to the pyramids has long been a mystery.

Researchers have uncovered a now-dried-up branch of the Nile that came right up to the great pyramid complex of Giza about 4,500 years ago.

The findings, published in the Proceedings of the National Academy of Sciences on Monday, explain how ancient Egyptians were able to haul millions of the tons-heavy building blocks to the site of the iconic pyramids over four miles of what is now a desert landscape.

"It was impossible to build the pyramids here without this branch of the Nile," study author and geographer Hader Sheesh said, per The New York Times.

A 4,500-year-old architectural marvel that still baffles scientists

Awesome in size, with perfect geometry, and adorned with intricate decorations, the pyramids at Giza, on the outskirts of modern Cairo, served to demonstrate the power of the pharaohs in Egypt's golden age.

The site comprises three pyramids and the Great Sphinx of Giza, built as ornate, awe-inspiring mausoleums for pharaohs Khufu, Khafre, and Menkaure between about 2560 B.C. and 2540 BC.

Khufu's pyramid, known as the Great Pyramid, was the first to be built and the biggest of the three. It comprises an estimated 2.3 million blocks of limestone and granite. Each block weighs between 2.5 and 15 tons, per National Geographic.

The Great Pyramid is the oldest of the famed Seven Wonders of the Ancient World and the only one to remain largely intact. It initially rose about 481 feet, making it the world's tallest man-made structure for almost 4,000 years.

Yet the Nile is about four miles east of the pyramids. How builders at the time managed to transport the huge blocks to the pyramid building site has long puzzled scientists and archaeologists.

Detective work to discover a river bed

Scientists had already thought Egyptians may have brought the stones to the site by water.

A papyrus discovered in 2013 showed the location of an ancient harbor near the Red Sea where the stones were loaded, suggesting the Egyptians knew how to move the blocks along rivers.

Other digs had suggested a harbor was built next to the pyramids and that builders had carved intricate waterways near the port.

To determine whether the Nile followed a different path at the time, scientists dug holes in the desert surrounding the pyramids looking for ancient pollen from plants like papyrus and cattails, which thrive in an aquatic environment.

The study showed that during Khufu, Khafre, and Menkaure's rule, about 4,500 years ago, a stable branch of the Nile river stretched out towards the pyramids.

This branch is now long gone. Pollen from drought-resistant plants like grasses showed that this river branch had been dwindling for centuries by the time King Tutankhamun came to power, around 1350 B.C., per The Times.

"Knowing more about the environment can solve part of the enigma of the pyramids' construction," Sheisha said per the Times.