By Sarah Brown, CNN

(CNN) - Millions of Muslims began the Hajj pilgrimage in Saudi Arabia on Sunday, which represents one of the largest annual human gatherings on the planet.

The Hajj is one of the five pillars of Islam, a journey every Muslim is expected to take in his or her lifetime if the person is physically and financially able.

This year, the Saudi Arabian city of Mecca is hosting more than 2 million Muslims, about 1 million fewer than last year, according to the Associated Press.

Our iReport team has asked pilgrims who have performed the Hajj about how the experience changed them - and for their advice to those undertaking the pilgrimage for the first time.

The result is a mix of spiritual and practical life lessons that transcend Islam.

1. Patience

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