One of the Five Pillars of Islam requires every capable Muslim to perform the Hajj pilgrimage at least once in their lifetime. Multiple parts of the Hajj require pilgrims to walk several times around the Kaaba in a counter-clockwise direction (as viewed from above). This circumambulation, the Tawaf, is also performed by pilgrims during the Umrah (lesser pilgrimage). However, the most dramatic times are during the Hajj, when about three million (officially) pilgrims simultaneously gather to circle the building on the same day.