Muslims have for centuries made the pilgrimage to Mecca. But with the number ever increasing, the city has had to expand, sparking controversy about the effect on its holy sites.
The changing face of Haj
Of all the holy sites of the Islamic world, none is more sacred than Mecca, the Saudi Arabian city towards which all Muslims prostrate themselves during prayer.
The city is so holy that no non-Muslim is meant to enter its environs.
But Mecca, as these photographs show, is changing.
For century upon century it has been a place of pilgrimage, but as travel advances made it easier to reach, so the city has expanded, outwards and upwards, to accommodate the growing number of annual pilgrims.
Such growth has brought wealth, people and ideas but also controversy, as the architecture of the 21st century comes up against varying ideas of religious piety and purity.
Mecca holds a special place in the thoughts of Muslims. The Prophet Mohammed was born in the city and received his first revelation on one of the mountains surrounding it. Within the city is the Kaaba, the holiest site in Islam, which Muslims believe was built by the Prophet Ibrahim and his son.
As well as praying in the direction of the Kaaba, one of the five pillars of Islam is that, at least once in their lifetime, Muslims should make the Haj to the city.
This pilgrimage, more than any other single event, still defines the rhythm of the city. Over the years, Mecca has changed several times.
Unlike the Vatican City, the spiritual heart of Catholicism, Mecca has always been a working city in its own right.
This gave it a special character, similar to that of Varanasi, one of the holiest cities for Hindus and Buddhists, that of being both a place of work and a place of worship.
But the annual pilgrimage was still a focus. In the past, Meccans took pride in hosting pilgrims in their own homes, giving them lodging and food for the few days of the Haj.
This was the case as recently as the start of the 20th century, when the difficulty of international travel limited the total number of pilgrims.
More recently, pilgrims have rented the private homes of Meccans. These Meccans stand to earn a significant amount of rent for a couple of weeks, so will take holidays during Haj.
This has had a knock-on effect, with, for example, Indonesia benefiting from an annual boom in holidaying Saudis.
But the pressure of these visitors to the holy sites has changed Mecca.
Every year, about 12 million pilgrims visit the city. Year on year, the number is rising, both because Islam as a faith is expanding and because increased prosperity means more Muslims can afford the pilgrimage.
By 2025, the annual number of pilgrims is predicted to have increased to 17 million.
In recent years, two flagship projects were created to accommodate the increase in pilgrims but they have simultaneously changed the face of the city. The first and biggest was the enormous Abraj Al Bait project, directly overlooking the Kaaba. This complex of seven towers boasts a hotel, apartments, a mall and a medical centre.
It has 1.4 million square metres of floor space, more than four times the size of the Dubai Mall.
The building is dominated by the Mecca Clock Tower, an enormous clock face that, while reminiscent of Britain's Big Ben, is more than six times the size.
At night, the clock face is lit green, the colour of Islam, and an enormous crescent at the top is illuminated. Some Saudis have suggested the Mecca clock could supersede Greenwich Mean Time as the standard by which the world's time is set.
The second flagship project in the city began this autumn with the enlargement of the Grand Mosque.
The Saudi government is reportedly increasing the total size to 400,000 square metres, which would accommodate two million pilgrims instead of the current 900,000.
Very little information has been released about the expansion, which will irrevocably change the look of the mosque and the city.
What is known is that a new railway, estimated to cost $1.8 billion, will be built to link the various holy sites in the city.
Seen from the air, the changes reshaping Mecca are clearly visible.
The city is surrounded on all sides by hills and mountains, with the Grand Mosque set among homes and offices.
The Abraj complex dominates the skyline, seeming even to eclipse the mountains in scale. Such a man-made building overshadowing a monument to God has understandably raised controversy.
In particular, objections have been made about the removal of historical sites associated with the Prophet.
The background to this is two-fold. Firstly, there is the particular religious tradition from which Saudi's rulers stem, the version of Islam known as Wahhabism that frowns on any reverence of historical sites that could be seen as shrines.
The second element is a broader balancing of the responsibilities of the Saudi state towards the religious monuments in its care.
The rulers of Saudi Arabia have always had to tread a difficult line as both political and religious leaders, hence the title of the Saudi Arabian king as both ruler of the state and Custodian of the Two Holy Mosques.
The Saudis must also balance the traditional demands of a state, to organise infrastructure and decide the design of their buildings, with the recognition that they are the guardians of the two holiest sites in Islam.
Because of this, there are opinions within and outside Saudi Arabia on the best way to develop Mecca to be most in keeping with various interpretations of Islamic history.
The annual pilgrimage is an enormous logistical exercise. Millions of pilgrims from every continent converge on one medium-sized city.
The Saudi authorities have to ensure their safety, as well as make sure the infrastructure of water, waste, roads and airports function efficiently under the strain. The government maintains ambulances and first-aid teams and distributes free food and drink to pilgrims.
At the same time, the pilgrimage is religious, which means that the Saudis have to make sure that all the millions of pilgrims are able to perform all the necessary rites.
The infrastructure needed for all that is being built, but how it finally fits in with the character of the city is the subject of much debate.
In Mecca, the demands of the 21st century have come up hard against the ideals of a much older religion.
To fulfil the requirements of the faith, the Saudis are changing the face of their holiest city.