William Tolan/FOXNews.com

On the western bank of the Nile, where the sprawl of greater Cairo ends and the desert begins, the Pyramids rise out of the sand like three individual mountains. The largest is 2 1/2 football fields long at its base and some 80 stories high. Of the Seven Wonders of the World, they are the only survivors.

These man-made mountains were built as tombs 5,000 years ago by kings Cheops, his son Chephren and grandson Mycerinus, all of whom ruled ancient Egypt during the 4th Dynasty of the Old Kingdom.

The expertise and labor required to construct the Pyramids still boggles the mind. For the Cheops Pyramid, the largest, it took 10 years just to build the road and the earthen ramps that were used as a primitive form of scaffolding. According to Ashraf Mohedin, an archaeologist with the Egyptian Department of Antiquities and an expert on the Pyramids, it took another 20 years, with a workforce of more than 300,000, to construct the Pyramid itself.

The limestone came from local quarries and was cut into massive blocks, each weighing nearly three tons. Mohedin said the ancient Egyptian builders, using sleds, ropes and sheer muscle, hoisted a total of 2.5 million blocks to construct the Cheops pyramid. He pointed to a precision design that distributed weight evenly, utilized airshafts for ventilation and even aligned the structures with the stars for cosmological significance.

At one time the pyramids were entirely covered with a casing of polished white limestone, the remnants of which are still visible on all three. But over the centuries, Mohedin said, successive Arab rulers stripped away the outer casings and used the stones to build their own palaces. The result today is a jagged geometry of soft inner stones whose angles have been eaten away by time.

William Tolan/FOXNews.com

Inside the pyramids are a series of narrow passageways leading to ventilated burial chambers, whose royal occupants and possessions were long ago looted by grave robbers. Nearby are the tombs of various queens. In one underground complex, archaeologists discovered the wooden boat that carried Cheops' body across the Nile and which, it was believed, would ferry him to the afterlife.

In the shadow of the Great Pyramids, sits the Sphinx, the Greek name given to the enormous stone statue of a man's head on the body of a lion. According to Mohammed el Attar, another Egyptian archaeologist, the man depicted on the Sphinx is none other than King Cheops himself, who ordered the statue carved from the rock left over from the construction of his pyramid.

There are various legends about what happened to the Sphinx's nose and beard. One says that during Napoleon's brief occupation of Egypt in 1798, his soldiers used the Sphinx for target practice and blasted them off. Others say it was the occupying Ottoman Turks who did the shooting. Egyptian archaeologist Mohedin believes the most plausible culprit was an Abassid conqueror who tried to destroy the face because it violated Islam's injunction against graven images.

Whoever was responsible, British adventurers in the 19th century carried off a part of the beard to London, where it now sits in the British museum. The whereabouts of the Sphinx's nose remains unknown.

Perhaps the most stubborn controversy surrounding the Pyramids centers on who actually performed the back-breaking physical labor to build them. Many still believe it was the ancient Hebrew slaves, whose bondage in Egypt is recorded in the Bible.

But Egyptologists dismiss this theory, noting the Pyramids were already more than 1,000 years old when the Pharaoh Ramses II enslaved the Hebrews. Moreover, the recent discovery of tombs in the desert near the Sphinx indicates the workers weren't Egyptian slaves either, but rather a highly skilled army of surveyors, architects and mathematicians, along with paid masons and laborers.

"Some people think the Pyramids were built by people from outer space, and others think they were built by slaves," laughed Mohedin. "Those are good stories, but neither is true."