More than 2 million Muslims have begun the annual Hajj pilgrimage to Mecca, Islam's holiest city, in Saudi Arabia, Al Jazeera reports.

Why it matters: Every able-bodied Muslim is required to take part in the five-day pilgrimage at least once in their life to visit the Kaaba, a cube-shaped building considered the holiest site in Islam, and perform a series of other holy rituals.