he Pyramids of Giza are the oldest of the Seven Wonders of the Ancient World.

Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more.(CNN)New evidence about the Nile bolsters a long-standing theory of how ancient Egyptians managed to build the massive pyramids of Giza thousands of years ago.Researchers led by geographer Hader Sheisha at Aix-Marseille University in France used paleoecological clues to help reconstruct what Egypt's Nile river might have looked like over the past 8,000 years.They determined the pyramid builders likely took advantage of a "now-defunct" arm of the river to move construction materials, according a study published August 24 in the Proceedings of the National Academy of Sciences.Their findings show "that the former waterscapes and higher river levels around 4,500 years ago facilitated the construction of the Giza Pyramid Complex," the study said.The Great Pyramid stands about 455 feet high and was commissioned by Pharaoh Khufu in the 26th century BC. Comprised of 2.3 million stone blocks with a combined mass of 5.75 million tons (that's 16 times more than the Empire State Building), it's the largest of the group of pyramids at Giza. The other two main pyramids belong to Khufu's son Khafre and grandson Menkaure.Built on the Giza plateau bordering Cairo, the structures -- surrounded by temples, cemeteries and workers' quarters -- are the oldest of the Seven Wonders of the Ancient World.

Scientists have long theorized that ancient Egyptians must have exploited former parts of the Nile to move the tons of limestone and granite required to build the giant structures. (The Nile's current waterways have moved too far away from the pyramid sites to be of use.)

This explanation, known as the "fluvial-port-complex" hypothesis, posits that ancient Egyptian engineers cut a small canal across from the site of the pyramid to the Nile's Khufu branch, along the river's western edge of the river's flood plain, and dredged basins down to the river's bottom. The annual flood waters functioned like a hydraulic lift, allowing them to move massive blocks of stone to the construction site, the researchers said.