 Complete the following phrase:  Mecca has been the site of several incidents and failures of crowd control because of the large numbers of people who come to make the Hajj. For example, on 2 July 1990, a pilgrimage to Mecca ended in tragedy when the ventilation system failed in a crowded pedestrian tunnel and 1,426 people were either suffocated or trampled to death in a stampede. On 24 September 2015, 700 pilgrims 