FOR more than four millennia, they have stood among the desert sands as a testament to the engineering brilliance of ancient Egypt.
But the great pyramids and the Sphinx, the last of the seven wonders of the ancient world to remain intact, are at risk of destruction from water, a new study has confirmed.
Scientists at Egyptian and US universities have found that farming, urbanisation and housing near the temples at Giza are causing water tables to rise and threaten the future of the ancient monuments.
Preliminary findings from a joint study by the University of California and the University of Sohag, in Egypt, indicate that when the water table rises, the groundwater comes closer to the foundations, columns and walls of the antiquities. The salt in the water weakens the stone and causes structural damage.
Dr Ayman Ahmed, of Sohag University, said: "Probably the most dangerous factors affecting the pharonic monuments are urbanisation and agricultural development."
Damage to the monuments has been accelerated in the years since the completion of the Aswan Dam, which has allowed year-round irrigation of crops instead of seasonal flooding, leading to more ground water in the system.
Together with Graham Fogg, a professor of hydrology at the University of California, Dr Ahmed hopes to find ways to prevent and reduce the damage to the ancient relics by building a computer model of how ground water moves under the monuments, using data from sites including the Sphinx and the temples at Karnak and Luxor.
Cracks have recently widened in the face of the Sphinx, and experts have become increasingly worried that the head of the relic, which is more than twice the age of Christianity, is in danger of toppling.
It has also been found that previous attempts to repair the damage have compounded the decay.
In the 1980s, a carefully planned restoration of the Sphinx was in progress. Over six years, more than 2,000 limestone blocks were added to its body and chemicals were injected into it. However, the treatment did not work, only serving to trap existing moisture in the rock, and the additional blocks flaked away, along with parts of the original rock. Later, many workers who were not specifically trained in restoration laboured for six months to repair the damage, but, again, their attempts appeared to exacerbate the crumbling process and in 1988 the left shoulder crumbled and blocks fell off.
The name Sphinx, meaning strangler, was first given by the Greeks to a fabulous monster with a woman’s head and a lion’s body. According to archaeologists, it appears to have started in Egypt in the form of a sun god and gradually had been adapted to wearing the head of a king in full ceremonial dress.
The Great Pyramid at Giza was built by the Egyptian pharaoh Khufu around 2560 BC to serve as a tomb when he died. It was the tallest structure on Earth for more than 43 centuries, only to be surpassed in height in the 19th century AD.
The structure consists of about two million blocks of stone, each weighing more than two tons.
It has been suggested that there are enough blocks in the three pyramids to build a three-metre high, 0.3-metre thick wall around France.
Dr Nigel Strudwick, an antiquities keeper at the British Museum’s department of Ancient Egypt and Sudan, said: "This water table problem is something that we have been worried was happening for many years.
"If the water table rises, the monuments, which are made of limestone, are very porous and will absorb it.
"When they are exposed to water and humidity, they do various things like collapse, exfoliate and effloresce salts,a Dr Strudwick added.
"If efflorescence occurs, it means salt crystals start growing on the surface of the rock, and if there is anything sitting on top of that, like some decoration, then it just gets pushed off and crumbles."
He added: "The Egyptians are very concerned and this report confirms what everybody has been worried about for a number of years.
"It is important that we now get more scientific research to back this up."
Modern pretenders, great achievements
ALTHOUGH the seven original "wonders of the world" may have crumbled through many centuries of neglect and natural erosion, several achievements spanning the last 1,500 years are widely identified as deserving of the moniker.
Built between 1630 and 1648 by the emperor Shah Jahan as a mausoleum for his wife Mumtaz Mahal, the Taj Mahal is a marvel of architectural elegance.
The Great Wall of China was originally built to keep out nomadic invaders from the north, most of the present wall was constructed during the Ming dynasty (1368 - 1644). Altogether, the wall winds for 1400 miles across northern China and has an average height of 23 feet.
The Easter Island Statues are colossal elongated heads, up to 32 feet high, carved from volcanic rock. The South Pacific island on which they stand was discovered on Easter Day 1722 by the Dutch explorer Jacob Roggeveen - the statues were probably made by the ancestors of its Polynesian inhabitants.
The Eiffel Tower was built for the 1889 Paris Exhibition by the French bridge engineer Alexandre Gustave Eiffel.
The Mayan City of Tikal in Central America is the ceremonial centre of the Mayan empire, dating from about 300 BC and was rediscovered in 1848 in northern Guatemala.
Chartres Cathedral, dating from the 12th century AD, stands on a hill overlooking the French market town.
And completed in 1914 at a cost of 300 million, The Panama Canal was constructed in just ten years. A ship travelling from New York to San Francisco can save 7,872 miles using the canal instead of going around South America.