The peak of the Muslim religious rites comes on 31 January, when worshippers climb nearby Mount Arafat, where the Prophet Muhammad preached his last sermon.
The number of people making the hajj has increased year by year as modern transportation and organization have eased what used to be a difficult journey. But Saudi officials say this year's number is slightly lower than last year's peak of just over 2 million.
Devout followers of Islam must openly profess their faith, pray five times a day, give alms, and fast from dawn to dusk during the holy month of Ramadan. Those that are physically and economically able must also make the hajj at least once in their lifetime.
The pilgrimage is an essential aspect of a Muslim believer's religious duties. But, as two-time Kyrgyz pilgrim Hajji (Hajji is the title for anyone who has made the pilgrimage) Abdyjapar Alymsak-uulu told our correspondent last year, the pilgrimage is also central to a Muslim's secular life. "The hajj has a big role in growing up, because when you make the pilgrimage it does not matter where you work, what kind of profession you have. When you wear the ikram [a special garment for hajj pilgrims], it doesn't matter whether a person is poor, wealthy or a king. Everybody is equal," Alymsak-uulu said.
The Prophet Muhammad established Islam 14 centuries ago in what is now Saudi Arabia. Since then, the faith has spread from West Africa to the Philippines along a band encompassing East Africa, Central Asia and western China, Malaysia, and Indochina. It has 4.5 million followers in North America and nearly 32 million in Europe.
Like Christianity, the world's largest religion, Islam is not a monolith. It has two major divisions, the majority Sunni and the smaller Shi'a. Within these divisions, there are various permutations, from the ultraconservative Wahhabis of Saudi Arabia and the highly politicized bodies -- such as the Taliban, Afghanistan's former ruling militia -- to groups elsewhere whose observance of the faith is less extreme.
In the early centuries of Islam, the pilgrimage to Mecca was only for those few within reasonable reach of Mecca or for unusually hardy souls who could afford the months and resources required to trek on foot and by camel caravan to the Arabian desert kingdom. But with the immense growth of Islam and the advent of highways and airliners, the number of pilgrims has bloomed from thousands to hundreds of thousands to millions. The hajj has emerged as a major unifying force of Islam.
But the ease of modern travel is contributing to conditions that make the hajj difficult in a new way. So many pilgrims press into the towns and terrain around Mecca that feeding and sheltering them -- not to mention protecting them from fire, disease, stampedes, and riots -- challenges the ingenuity of the Saudi hosts. Saudi authorities have spent millions of dollars on sturdy tent cities and infrastructure. They employ tens of thousands of people to manage the secular organization of the event.
The year's events have added to the problems. Two terrorist bombings jolted Saudi Arabia in the last year and the Saudi have arrested dozens of people they say are connected to the Al-Qaeda network of Osama bin Laden, himself a Saudi, though in exile.
Typical of the pilgrims is a group of Kazakh Muslims who last year traveled to Saudi Arabia on a charter flight arranged by Kazakhstan's Department of Religion and the Kazakh Sputnik Travel Agency. The oil-rich Saudi Arabian government annually subsidizes travel to Mecca for Muslims from around the world, but this Kazakh group was one of many paying its own way. It was but one of the trickles that grow into a torrent of Muslim travelers from around the world.
Imam Kalizhan Zankoev of the Astana City Mosque said hajj travelers are of all ages. "I know an elderly women here in Astana. She is in her 70s and she went to hajj for the ninth time this year," he said. "She told us that her children help her [financially] to go there every year and she says that anyone who goes there once will want to visit that holy place again and again."
Cleric Bagdad Adukarimov, the naib, or deputy, imam of the Central Mosque in the Kazakh capital Astana, emphasized the spiritual focus of the hajj: "In Islam, the hajj pilgrimage is one of the most important five duties. Every Muslim who can afford the pilgrimage in terms of finance and health should go to the holy places of Mecca and Medina at least once in his lifetime. By going there, a Muslim purifies himself from all the sins and misdeeds made intentionally or unintentionally in the past."
Prophet Muhammad established the highly symbolic customs of the hajj as it is practiced today. But Islamic writings teach that the pilgrimage to Mecca itself dates to the Prophet Abraham, the father of humanity in ancient Jewish scripture. Islamic teachings say that in the centuries after Abraham, idolatry and pagan customs contaminated the hajj. Muhammad's reforms abolished the false practices.
One symbolic rite of the hajj occurs when the pilgrims gather at Medina to cast stones at three pillars representing Satan's three failed efforts to tempt Abraham to defy God's -- or to Muslims, Allah's -- commandments. This ceremony also typifies one of the modern problems of the hajj.
The crush of pilgrims seeking to stone Satan has grown so severe that the Saudis have had to adopt stringent crowd-control regulations, as they have everywhere else in the holy region.
(RFE/RL's Kyrgyz and Kazakh services contributed to this report.)