Hajj, one of the Five Pillars of Islam, is a religious obligation involving rituals and acts of worship that every Muslim must fulfil if they have the financial means and are physically able to do so.

More than 1.5 million foreign pilgrims have arrived in Saudi Arabia for this year’s Hajj, according to a government spokesperson on Wednesday. Hajj Ministry spokesperson Ghassan al-Nuwaimi provided an approximate number for foreigners at this year’s pilgrimage, though he did not specify how many domestic pilgrims were participating. Last year, there were 1,611,310 pilgrims from outside the country.

On Wednesday, worshippers streamed into Arafat, with some undertaking the journey on foot and carrying their luggage in temperatures nudging 40 degrees Celsius (104 Fahrenheit).

According to traditional sayings of the prophet, the Day of Arafat is the most sacred day of the year, when God draws near to the faithful and forgives their sins.

Mount Arafat, a rocky hill southeast of Mecca, holds immense significance in Islam. Arafat is mentioned in the Quran and it is where the Prophet Muhammad is said to have given his last sermon on his final Hajj.

Pilgrims remain in Arafat, in prayer and reflection, from after midnight until after sunset.

After sunset, they will head to Muzdalifah, halfway between Arafat and the sprawling tent city of Mina, where they will gather pebbles so they can perform the symbolic “stoning of the devil”.

Saudi Arabia has spent millions of dollars on crowd control and safety measures, but the sheer volume of participants continues to pose challenges. In recent years, one of the greatest difficulties has been the high temperatures.

Earlier this week, Health Minister Fahad bin Abdulrahman Al-Jalajel stated, “10,000 trees have been planted to provide more shade, there is increased hospital bed capacity, and the number of paramedics has tripled.”

Authorities have urged pilgrims to remain inside their tents between 10am (07:00 GMT) and 4pm (13:00 GMT) on Thursday when the desert sun is at its harshest. To combat the heat, fans spraying mist and providing cool air have been placed at the foot of the mount.