Large numbers of Muslims converge once a year on Saudi Arabia to unite in a series of religious rituals and acts of worship as they perform the Hajj, the pilgrimage that is one of the pillars of Islam.

Here is a look at the hajj, one of the largest mass gatherings in the world, which starts in Saudi Arabia on Wednesday.

Authorities have ratcheted up anti-heat measures such as extra shade to avoid a repeat of last year, when 1,301 people died as temperatures hit 51.8C (125.2F).