Despite the fact that the Great Pyramid is the largest and most spectacular in Egypt, it has always been empty, with no trace whatsoever of its creator, the Pharaoh Cheops, or of the royal treasures and artefacts Egyptologists assume he took with him to his grave.
But the scientists whose robot camera has discovered what they believe to be a secret chamber hidden at the end of a 65-metre (71yd) long passageway inside the pyramid were looking not for buried treasure, but for ways of protecting the six-million ton structure from human pollution - the 20 grams of water left behind by the breath and perspiration given off by each tourist.
The German team, led by a robotics expert, Rudolf Gantenbrink, had been investigating passageways in the hope of learning more about the circulation of the pyramid's air.
Working under the auspices of the German Archaeological Institute in Cairo, and financed by German and Swiss high- tech equipment companies Gore-tex, FES and Portescap, they had guided their book- sized robot a full 65 metres along the passageway up a 45- degree slope until, to their amazement, the video camera it carries showed that the corridor was blocked by a little stone door complete with large copper handles.
The pictures transmitted back suggest that the door, possibly made of alabaster or yellow limestone, is of a portcullis design, and can be opened by being slid upwards into a cavity. There is further evidence suggesting that behind the door lies a substantial, long- hidden chamber.
The pictures revealed a scatter of fine black dust in front of a 2mm-wide gap between the stone door and the wall. The dust cannot be from the white and yellowish stonework of the passageway (the last few metres of which is very finely made), but would be a typical product of decaying organic material, especially wood and textiles. Tutankhamun's and other Egyptian tombs have yielded huge numbers of wooden objects and textiles, including coffins and cloth used to wrap mummified corpses.
The fact that black dust from the chamber has been blown out of it implies the existence of air currents within the mystery room, which in turn suggests that it is of substantial size.
What is more, its geometric location within the pyramid hints at a large size. It stands exactly 21.5 metres (23.5yds) higher than the largest previously known chamber within the pyramid, the King's Chamber, which is in turn exactly 21.5 metres higher than the second-largest known chamber, the Queen's Chamber. As the diagram on page one shows, the passageway leading to the newly-discovered chamber rises at 45 degrees from the back of the Queen's Chamber.
All this is leading some experts to suspect that the mystery chamber could be the final resting place for the treasures or even the body of the Pharaoh Cheops.
It has been possible to gain access to the two main chambers in the pyramid for hundreds of years. They are completely empty, apart from the empty sarcophagus in the King's Chamber. Archaeologists still do not know for sure if the chambers were once packed with artefacts that were subsequently thoroughly looted, or whether the two chambers have always been empty.
It is notable that no antiquities or precious goods circulating in Egypt have ever been positively identified as having come originally from the Great Pyramid; if it had been profitably looted in the past, it is reasonable to suppose that this would not be the case.
This may mean that the mystery chamber contains a treasure every bit as stunning as that of Tutankhamun's.
The scientific team will now work to create a modified version of their robot, with an extendable arm capable of inserting a fibre-optic lens and light source through a gap in the stonework and into the space beyond. They hope to achieve this later this year.