The level area surrounding the hill is called the Plain of Arafat. The term Mount Arafat is sometimes applied to this entire area. It is an important place in Islam because during the Hajj, pilgrims spend the afternoon there on the ninth day of Dhu al-Hijjah (ذو الحجة). Failure to be present in the plain of Arafat on the required day invalidates the pilgrimage. Many pilgrims stay here all night in vigil. After Arafat, pilgrims of the Hajj head to Muzdalifa.