At least 1,300 people died during the annual hajj pilgrimage in Mecca this year. It was unclear whether the death toll was higher than usual, as each year pilgrims die from heat stress, illness and chronic disease.

But the toll has raised questions about whether Saudi Arabia made adequate preparations for intense heat and the influx of unregistered pilgrims who, the authorities say, relied on illicit tour operators to skirt the official permit process.

Here’s what to know about this year’s hajj.

What is the hajj?

The hajj, a pilgrimage in Saudi Arabia, is one of the five pillars of Islam, and all Muslims who are physically and financially able are obliged to perform it at least once in their lives.

People spend years saving up to travel to Mecca, the holiest city in Islam, to embark on the five-day pilgrimage, which takes place in the days before and during the holy period of Eid al-Adha. Pilgrims visit several holy sites, including circling the Kaaba and praying near Mount Arafat.