The Sacred Mosque (al-Masjid al-Haram) in Mecca, commonly described as the largest mosque in the world, and the pilgrimage it gathers — the Hajj, one of the Five Pillars of Islam, a duty owed once in a lifetime by every able and able-to-afford Muslim. At its center stands the Kaaba, the cube toward which Muslims everywhere turn to pray, and around it each year flows one of the largest recurring gatherings of humanity on earth, a coordinated rite of consecration, circling, and standing that erases rank and binds a global community for a few sacred days.
For a few days each year, as many as two million Muslims of every nation and language converge on a single point in the Arabian desert and strip off the markers of wealth. The men wrap themselves in two plain white cloths; the women join the same rite in plain, modest dress. A king and a laborer become indistinguishable. They walk the same path, speak the same words, and circle the same ancient cube. The Hajj is the rare human event engineered to dissolve hierarchy on a mass scale, and it has done so, year after year, for fourteen centuries. The challenge of moving that many bodies through one small valley on one schedule is also, in our own time, one of the hardest problems of engineering and crowd management anywhere on the planet.