<P> On 11 September 2015, at least 111 people died and 394 were injured when a crane collapsed onto the mosque . </P> <P> The Great Mosque is the main setting for the Hajj and' Umrah pilgrimages that occur in the month of Dhu al - Hijjah in the Islamic calendar and at any time of the year, respectively . The Hajj pilgrimage is one of the Pillars of Islam, required of all able - bodied Muslims who can afford the trip . In recent times, over 5 million Muslims perform the Hajj every year . </P> <P> Some of the rituals performed by pilgrims are symbolic of historical incidents . For example, the episode of Hagar's search for water is emulated by Muslims as they run between the two hills of Safa and Marwah . </P> <P> The Hajj is associated with the life of the Islamic prophet Muhammad from the 7th century, but the ritual of pilgrimage to Mecca is considered by Muslims to stretch back thousands of years to the time of Ibrahim (Abraham). </P>

What are the names of the two hills that the pilgrims visit