The five core days trace a loop of sites outside Mecca, each connected to a moment in the tradition. It begins on the 8th of Dhu al-Hijjah, when pilgrims don the ihram - two pieces of unstitched white cloth for men, modest white covering for women - and walk to Mina, a valley about 10 km from central Mecca. Mina is the city of tents: more than 100,000 air-conditioned tents that appear at Hajj and disappear after. On the 9th, the Day of Arafah, pilgrims move another 15 km to the plains of Arafat and stand in vigil until sunset; a pilgrim's Hajj is considered invalid without this afternoon. At dusk they move to Muzdalifah and sleep under the stars, gathering pebbles for the next morning. The 10th begins Eid al-Adha, the great feast. Pilgrims proceed to the Jamarat Bridge to stone the pillars that represent the devil, offer a sacrifice (most purchase a voucher), perform Tawaf and Sa'i around the Kaaba, and move back to Mina for the remaining days of stoning.

The Saudi government operates a Ministry of Hajj and Umrah to manage what is, by any measure, the world's largest recurring logistical puzzle. Quotas are allocated to Muslim-majority countries - pilgrims from those nations can wait years for a slot, while citizens of countries with small Muslim populations often secure a Hajj visa in weeks. The Al Mashaaer Al Mugaddassah metro line, Saudi Arabia's first, was purpose-built to shuttle pilgrims between the holy sites and is the highest-capacity metro line in the world - though even it gets crowded at peak. The Haramain High-Speed Railway now connects Mecca to Medina via Jeddah. In medieval times the journey from Morocco or Syria or Iraq took months, sometimes years, in camel caravans escorted by soldiers and physicians under an amir al-hajj. Muslim travelers like Ibn Jubayr and Ibn Battuta left detailed accounts of those journeys, and Sir Richard Burton famously made the Hajj in 1853 disguised as a Pashtun pilgrim and wrote a book about it.

Unless you are a Saudi citizen, you need a Hajj visa. The Hajj cannot be performed on a tourist visa. Many countries require you to apply through the local governing body of Islam, which allocates places under national rules. Some countries let you apply directly through the Saudi Nusuk portal. Evidence of Muslim identity may be required - a letter from a local mosque, for example. Proof of meningitis vaccination (ACYW135) is required between three years and ten days before arrival; yellow fever vaccination applies for those coming from yellow fever zones; polio vaccination is needed for children up to 15. Women over 45 are exempt from the mahram requirement provided they have written permission. Throughout Hajj, pilgrims remove signs of wealth and class - the white ihram is the visible equalizer, a king in the same two pieces of cloth as a porter.

Hajj's greatest danger has always been its scale. Between 1990 and 2015, at least 2,777 pilgrims were killed in crushes and stampedes. A fire in the tent city of Mina killed 340 in 1997. In 1987, security forces broke up an Iranian demonstration against the United States; 402 died. A construction crane collapse in 2015 killed 107, and later that year a stampede at the Jamarat stoning killed hundreds more - the worst in decades. Saudi authorities have since reconstructed the Jamarat area as a multi-level bridge to spread the crowds. The peril does not diminish the pilgrimage for those who make it; most pilgrims describe the experience in the language of transformation, not of fear. Among the dead over the decades have been pensioners who saved their lives' wages for the journey, whole families, village delegations. Their relatives often speak of them as having died at the closest place to God. That belief is part of what keeps the pilgrims coming.

Hajj visas restrict travel to Mecca, Medina, Mina, Arafah, and Muzdalifah. Additional travel permits for the rest of Saudi Arabia are difficult to obtain and rarely granted. Most pilgrims add a stop in Medina - the city where Muhammad lived, taught, and is buried - before flying home. Medina's dates, grown in the oases surrounding the city, are famously excellent. Pilgrims from carpet-producing regions often bring rugs to sell along the way to help finance their journey, and the bazaars of Jeddah carry weavings from the full breadth of the Muslim world. For the pilgrims, home is the point of return - Jakarta, Istanbul, Lagos, Bradford, Dearborn - and the Hajj is what they carry back. For the two million, those final minutes circling the Kaaba - the Tawaf Widaa, the farewell circumambulation - are the only time in their lives they will be in this place. Most leave believing that was enough.