There is a growing shadow being cast over Islam's holiest site. Only a few metres from the walls of the Grand Mosque in Mecca skyscrapers are reaching further into the sky, slowly blocking out the light. These enormous and garish newcomers now dwarf the elegant black granite of the Kaaba, the focal point of the four million Muslims' annual Haj pilgrimage.

The tower blocks are the latest and largest evidence of the destruction of Islamic heritage that has wiped almost all of the historic city from the physical landscape. As revealed in The Independent last August,the historic cities of Mecca and Medina are under an unprecedented assault from religious zealots and their commercial backers.

Writing in response to the article, Prince Turki al-Faisal said that Saudi Arabia was spending more than $19bn (£11bn) preserving and maintaining these two holy sites. "[We are aware] how important the preservation of this heritage is, not just to us but to the millions of Muslims from around the world who visit the two holy mosques every year. It is hardly something we are going to allow to be destroyed."

This rebuttal sits at odds with a series of previously unseen photographs, published today, that document the demolition of key archaeological sites and their replacement with skyscrapers.

Saudi religious authorities have overseen a decades-long demolition campaign that has cleared the way for developers to embark on a building spree of multi-storey hotels, restaurants, shopping centres and luxury apartment blocks on a scale unseen outside Dubai. The driving force behind this historical demolition is Wahhabism ­ the austere state faith that the House of Saud brought with it when Ibn Saud conquered the Arabian peninsula in the 1920s.

The Wahhabis live in fanatical fear that places of historical or religious interest could give rise to alternative forms of pilgrimage or worship. Their obsession with combating idolatry has seen them flatten all evidence of a past that does not agree with their interpretation of Islam.

Irfan Ahmed al-Alawi, the chairman of the Islamic Heritage Foundation, set up to help protect the holy sites, says the case of the grave of Amina bint Wahb, the mother of the Prophet, found in 1998, is typical of what has happened. "It was bulldozed in Abwa and gasoline was poured on it. Even though thousands of petitions throughout the Muslim world were sent, nothing could stop this action."

Today there are fewer than 20 structures remaining in Mecca that date back to the time of the Prophet 1,400 years ago. The litany of this lost history includes the house of Khadijah, the wife of the Prophet, demolished to make way for public lavatories; the house of Abu Bakr, the Prophet's companion, now the site of the local Hilton hotel; the house of Ali-Oraid, the grandson of the Prophet, and the Mosque of abu-Qubais, now the location of the King's palace in Mecca.

Yet the same oil-rich dynasty that pumped money into the Taliban regime as they blew up the Bamiyan Buddhas in Afghanistan six years ago has so far avoided international criticism for similar acts of vandalism at home. Mai Yamani, author of The Cradle of Islam, said it was time for other Muslim governments to ignore the al-Sauds' oil wealth and clout and speak out. " What is alarming about this is that the world doesn't question the al-Sauds' custodianship of Islam's two holy places. These are the sites that are of such importance to over one billion Muslims and yet their destruction is being ignored," she said. "When the Prophet was insulted by Danish cartoonists thousands of people went into the streets to protest. The sites related to the Prophet are part of their heritage and religion but we see no concern from Muslims."

Lay people, and in some cases even US senators could be forgiven for thinking that the House of Saud has been the guardian of the two holy places for time immemorial. In fact, it is only 80 years since the tribal chieftain Ibn Saud occupied Mecca and Medina. The House of Saud has been bound to Wahhabism since the 18th century religious reformer Mohamed Ibn Abdul-Wahab signed a pact with Mohammed bin Saud in 1744. Wahab's warrior zealots helped to conquer a kingdom for the tribal chieftains. The House of Saud got its wealth and power, and the clerics got the vehicle of state they needed to spread their fundamentalist ideology around the world. The ruler of this fledgling kingdom needed the legitimacy afforded by declaring himself " custodian of the two holy places".

But that legitimacy has come at an enormous price for the diversity of Muslims who look to Mecca for guidance. Once in charge, the Wahhabists wasted little time in censoring the Haj. As early as 1929, Egyptian pilgrims were refused permission to celebrate the colourful Mahmal rites and more than 30 were killed. At the time Egypt severed diplomatic relations with Saudi Arabia. Few governments have stood up to them since.

Instead, the homogenisation of Islam's holiest sites was allowed to accelerate into a demolition campaign that now threatens the birthplace of the Prophet itself. The site survived the early reign of Ibn Saud 50 years ago when the architect for the planned library persuaded the absolute ruler to allow him to preserve the remains under the new structure. Saudi authorities now plan to "update" the site with a car park that would mean concreting over the remains.

"The al-Sauds need to rein in the Wahhabists now," warns Dr Yamani. "Mecca used to be a symbol of Muslim diversity and it needs to be again." But with oil prices and profits, at record highs, there is little sign the House of Saud is listening.

Sami Angawi, a Hijazi architect who has devoted his life to a largely doomed effort to preserve what remains of the history of the world's greatest pilgrimage sites, said that the final farewell to Mecca was imminent. " What we are witnessing are the last days of Mecca and Medina."

Mecca's skyline

Giant cranes and half-constructed skyscrapers tower over the Grand Mosque in Mecca. Six new property developments, including the Bin Laden group's Zam Zam Tower, are transforming the character of Islam's holiest city

ISLAMIC HERITAGE FOUNDATION

Mountain of light

The mountain of light, or al-Nour, is next in the Wahhabis' sights. Home to the Hira'a cave, it was here that the Prophet is said to have received the first verses of the Koran. Hardline clerics want it destroyed to stop pilgrims visiting. At the foot of the hill there is a Wahhabi fatwa: " The Prophet Mohamed (PBUH) did not permit us to climb on to this hill, not to pray here, not to touch stones, and tie knots on trees..."

ISLAMIC HERITAGE FOUNDATION

The Prophet's wife's grave

The ruins in the foreground are the remains of the grave of the Prophet's wife, Al Baqi, destroyed in the 1950s. The mutawi religious police are present night and day to prevent anyone placing flowers on the site, or even praying in the proximity of the graves

THE ISLAMIC HERITAGE FOUNDATION

Al Oraid Mosque

The 1,200-year-old mosque, site of the grave of the Prophet's grandson al-Oraid, is seen here being dynamited. Gathered around the site are Saudi religious police with their distinctive red scarves, who appear to be celebrating

THE ISLAMIC HERITAGE FOUNDATION