Jim Muir in Cairo looks back on four and a half millennia of history

The work was carried out to undo some of the damage done by exposure to mass tourism.

The Great Pyramid of Cheops - of Khufu - was reopened by Egypt's tourism minister, Farouk Hosni, on Thursday, along with three newly-opened tombs and the world's oldest sun temple at the nearby Sphinx.

"We want the world to know that Egypt looks after its antiquities," Mr Hosni told reporters gathered on the Giza plateau. "But we also want to protect our monuments from its many visitors."

Tourists put up with 80% humidity in Cheops' passages before ventilation system

The Pyramids are the only one of "Seven Wonders of the Ancient World" to have survived into the modern era and they provide a welcome source of national income for Egypt.

But the huge number of tourists visiting the Giza plateau brings its own problems.

Humidity levels in the tunnels and chambers inside the Great Pyramid had reached 80% because of the sheer volume of people going in.

The condensation caused a build-up of salt on the pyramid's 4,500-year-old stone walls, leading to flaking and cracks.

Restoration programme

For the past 14 months, experts have been treating the damage and also removing grafitti carved into the walls by visitors.

New lighting and ventilation systems have been installed, the latter changing the air inside every 45 minutes, reducing humidity and carbon-dioxide levels.

Security cameras will make sure no future tourists will leave their mark on the ancient monument.

New surveillance equipment to complement more traditional methods

In addition to the new fixtures, two burial chambers inside the 140-metre (450ft) tall pyramid were opened for the first time, after protective measures were taken.

From now on only 300 visitors a day, 150 in the morning and 150 in the afternoon, will be allowed to enter the newly-refurbished pyramid. And to prevent further damage from vibration, airliners are being banned from over-flying the site.

The authorities have now gone a long way towards preparing the Giza plateau for the coming of the year 2000.