Millions of Muslims from more than 100 countries descend on Mecca, or Makkah, in western Saudi Arabia, near the Red Sea, for this very special pilgrimage. This year the Saudi Arabian authorities have recorded 1.5 million arrivals.
Many of them will visit Medina as well, where Prophet Mohammed's mosque is located.
Islam requires able-bodied Muslims who can financially afford the pilgrimage to perform the Haj at least once.
Image: A view of Friday prayers in Mecca.
Also See: Under the crescent moon