Hassan Ibrahim, the director of the Muslim Public Affairs Council in Washington, has been on the hajj eight times. He says the common form of dress is a great equalizer. "You wouldn't see titles, you wouldn't identify who is richer or poorer, who is of a different class in his country or tribe, from whatever," he said. "Equality is pretty much the first thing that comes across."
One of the first rituals -- and also the last -- is called the Tawaf, or the Turning. A sea of humanity, all in white, circles counter-clockwise seven times around the square, stone building at the center of the Grand Mosque in Mecca.
That central structure is the Kaaba, the holiest shrine of Islam, which Muslims face toward when they pray, wherever they are in the world. It is believed it was built by the Prophet Ibrahim (Abraham) and his son, Ismail, and contains the Black Stone, which the faithful say was brought to Earth by the angel Jibril.
Ibrahim says that performing the Tawaf is a physical challenge that becomes more difficult, the closer you get to the Kaaba. "If you are closer to the center, the circle you are making is much smaller than somebody who is doing it 100 meters outside the center and it becomes sometimes a very tiring physical activity," he said.
Then, there is the Sa'i -- traveling seven times between the Marwah and Safah hills. This commemorates the search for water in the desert by the Prophet Ibrahim's wife, Hajar, after she was left alone with the baby, Ismail.
After Friday prayers in Mecca, the great mass of pilgrims makes their way over about 10 kilometers to the Valley of Mina, which is turned into a giant tent city, framed by mountain peaks. Crowds chant in a chorus, "Here I am Allah, answering your call." This year, the Saudi government provided some 20,000 buses for transportation for those not making the journey on foot.
One pilgrim from the African nation of Chad said that he is praying for peace, especially in the Middle East. "We pray for Muslims, the Iraqis present, we pray for all of them, for peace to come to Arab nations," he said. "We don't want conflicts to happen in all these places -- Israel, Palestine, all of them. We are praying for peace for them."
After spending the night in Mina the pilgrims make their way about 10 kilometers to Mount Arafat, where Muhammad delivered his last sermon in the year the 632 A.D., three months before his death.
Ibrahim says that, at Mount Arafat, Muslims come to ask God for forgiveness and to reaffirm their faith. He also explained that Mount Arafat has further significance, from the Koran's story of Adam and Eve. "After God forgave them [Adam and Eve], that is where they met again and, with their meeting, humanity on this Earth began. So we are kind of, in the sense of that legend, we are gathering again in that place to start life again as they have started life on Earth when God intended for it to be."
Ibrahim says the large number of people on the hajj must follow a very tight schedule of activities and it is no easy matter for all of them to move to the right place at the right time. "After sunset [Saturday], everybody moves from this Valley of Arafat, moving toward Mecca and by a certain hour, at like midnight, they move toward another point closer to Mecca," he said. "So, logistics-wise, it is a nightmare for anybody to try to move 2 million people."
The people camp on Saturday night at Muzdalifa, halfway between Mount Arafat and Mina.
On Sunday, the travelers return to Mina, where they throw seven pebbles each at three stone pillars, called Jamrah. Stoning the pillars represents Satan being driven off by the Prophet Ibrahim, his wife, and his son Ismail, for trying to tempt them into to disobeying God's command that Ibrahim sacrifice his son. The people throw the stones to symbolically ward off their own temptations.
Ibrahim says that because so many people are moving through a relatively tighter area, this is another difficult, and sometimes even dangerous part of the hajj. "You basically have human waves moving and if they are not directed in a reasonable way, you basically have a stampede, which happens from time to time," he said.
Fourteen people were killed during a stampede near the pillars last year and other stampedes have killed hundreds of others in previous years.
The stoning of the pillars is followed by the slaughter of an animal, usually a sheep, to mark the beginning of a three-day holiday called Eid al-Adha or Feast of Sacrifice. This feast is observed by Muslims around the world.
After the feast begins, pilgrims may return to Mecca and also travel again between Marwah and Safa. They can drink from the well of ZamZam, near the Kaaba, which is said to have sprung up under Ismail as his mother searched for water in the desert. They return to spend the night in Mina, where they will pray and perform the Jamrah stoning rituals again on the fourth and fifth days of the hajj.
Ibrahim says that the journey may be long and physically demanding, but the focus on God and spiritual renewal makes one forget all the difficulties. "The physical tiredness is, really, not the first thing on your mind. It is really that you are seeing yourself in the sight of God. You are not just conducting a physical activity," he said. "You are constantly in prayer, constantly asking for forgiveness for yourself, for the people you love, for humanity, in general, for peace on Earth."
To complete the hajj, everyone must perform the Tawaf around the Kaaba one last time on the fifth day. It is not required, but many pilgrims visit the tomb and mosque of the Prophet Muhammad in Medina before returning going home. According to the words of the prophet, if the hajj is performed properly, all previous sins are forgiven.