In order to accommodate the growing number of people making the pilgrimage to Mecca, required at least once of all Muslims who can afford it, Saudi Arabia is in the midst of enormous expansion projects in the holy city.

Most projects, from a new railway to a metro system, are expected to be completed by 2020, though a new King Abdulaziz International Airport and expansion of the Grand Mosque should be finished within the next two years, Mecca’s mayor told Reuters Friday.

"All of these projects are being developed to serve our guests and accommodate more of them," said Mecca’s mayor, Osama bin Fadl Al-Bar, according to Reuters.

The $100 billion expansion is part of the kingdom’s attempt to grow religious tourism in order to diversify its economy beyond oil, which has faced record low prices in recent years. The need for the extra space became tragically clear after a stampede of people completing Hajj, or pilgrimage, last year killed at least 719 people and injured 863 others in Mina, a village outside of Mecca.

Last year, 2 million Muslims from around the world descended on Mecca, doubling its population and crowding into the city and surrounding towns in temperatures that reached 110 degrees F. Some international governments, including Iran's, accused Saudi officials of incompetence in their crowd-control measures.

In reaction to the incident, King Salman of Saudi Arabia ordered a safety review "to improve the level of organization and management of the movement" of pilgrims.

Space issues should improve after expansion in Mecca is completed, say Saudi authorities. The Grand Mosque, the site of Islam's most sacred space, will be able to accommodate 2.2 million worshippers, up from 600,000 today. About 400,000 people per hour will be able to circle the sacred Ka'aba at the center of the mosque, Mayor Bar told Reuters.

The Jamarat bridge – the site of last year’s stampede and a pilgrimage site where visitors throw stones at pillars that symbolize the devil – will be able to handle up to half a million pilgrims per day, or 3 million over the course of the holy week.

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The city is also building dozens of new hotels and the world's biggest clock tower, as well as expanding transportation routes across the city, say officials.

This report contains material from Reuters.