Hundreds of thousands of pilgrims gather at the Grand Mosque in Mecca, Saudi Arabia, Nov. 3, 2011. Over 2.5 million Muslim pilgrims began their five-day Hajj here on Thursday night. The Mecca pilgrimage, also known as the Hajj, is a Muslim religious tradition that specifies that all able-bodied Muslims who can afford to travel to Saudi Arabia must visit Mecca at least once in their lives. (Xinhua/Wang Bo)