By growing demand and concerns for safety after deadly accidents, the Saudi government has been rapidly expanding Mecca’s hajj facilities to accommodate more pilgrims. At its peak in 2012, the hajj included 3.16 million pilgrims. But even at a rate of 3 million people per hajj, it would be impossible for all the world’s 1.8 billion Muslims to perform the Islamic duty of the pilgrimage in their lifetimes. In fact, for all Muslims who are alive today to perform hajj, it would take at least 581 years, The New York Times reported.

That’s just looking at the Muslims alive today — not accounting for future birth rates or for people who have already performed hajj, though a 2013 Pew survey of 39 countries found that 9 percent of Muslims had.

At least a quarter of pilgrims every year are citizens or residents of Saudi Arabia. The Saudi government sets quotas for every other country that sends pilgrims to the hajj based on its Muslim population.

Even countries with large Muslim populations can send only a small fraction of their citizens to the hajj. In Indonesia — which at more than 200 million has by far the largest Muslim population in the world — the wait time can range from seven to 37 years. Some countries complain that the quota allocation is not transparent enough, or that it should be based on demand rather than on Muslim population. The multiyear construction plan includes expanding the mosque around the Kaaba to hold 1.85 million people.

Here are some statistics about Hajj pilgrim 2018:

total pilgrims for 2018: 2,371,675

Domestic pilgrims for 2018: 612,953

Foreign pilgrims for 2018: 1,758,722

Some key figures:

– More than 2.37 million pilgrims are taking part this year, according to official figures.

– Tens of thousands of security personnel, including some 18,000 civil defence employees, are helping safeguard pilgrims, officials say. Thousands of security cameras have been set up along the pilgrimage route.

– Every hour, officials estimate an average of 107,000 pilgrims circle the Kaaba, the black cube at the centre of Makkah’s Grand Mosque, which Muslims around the world must face while praying.

– Twenty-five hospitals, 180 ambulances and more than 30,000 health practitioners have been prepped to provide emergency services to pilgrims, according to the hajj ministry.

– Tens of thousands of air-conditioned tents have been set up to house pilgrims as temperatures climb to 44 degrees Celsius (111 degrees Fahrenheit).

– Around 14,000 international and domestic flights have transported pilgrims to the kingdom, according to official figures. Some 21,000 buses have also brought the Muslim faithful to Makkah.

– 16,000 telecommunication towers and 3,000 WiFi zones have been set up to serve pilgrims, the hajj ministry says.

– Saudi Arabia says it plans to hand out eight million copies of the holy Koran in multiple languages to pilgrims along with other religious books.

– The kingdom hopes to welcome 30 million pilgrims annually in the kingdom by 2030. Muslims also travel to Saudi Arabia for the umra pilgrimage, which can be performed at any time of the year.

– Around 54 million pilgrims have attended the hajj over the past 25 years.