This week an estimated two million Muslims will descend on Mecca in Saudi Arabia, as the annual Haj begins.
The Saudi government has spent billions in recent years to improve safety and security after a stampede in 2015 killed thousands.
But this year the biggest concern isn't the crowds, it's the threat of cholera.
Saudi Ministry of Health spokesman Mashaal Abdelrahman Al-rabyan says precautions are being taken.
"The Kingdom of Saudi Arabia has provided all the cholera medication needed in case of reports of any cholera cases, whether inside the holy sites or at any of the border crossings. But so far we have no cases reported and we are able to handle any case which affects any of the pilgrims."
While there are no cases as yet, Saudi authorities are on edge as neighbouring Yemen battles what the United Nations has called the 'world's worst cholera outbreak'.
Latest figures state more than 1,700 people have died in Yemen since late April, with 5,000 new cases recorded each day.
It's estimated there are a total of 320,000 suspected infections so far this year, and this strain of the disease is capable of killing within hours.
Saudi health authorities say they are prepared, and Saudi Red Crescent official Ahmed Baryan says extra medical staff are on stand-by.
"We prepared ambulances all over Mecca and Medina but we are focusing now on Mecca as we had prepared 133 ambulance centres all over Mina and the Holy city."
The paramedics are in addition to around 100,000 security personnel.
Pakistani pilgrim Jabran Azghar says so far the pilgrimage has been highly organised, with electronic monitoring of the crowds.
"Before it was open for everyone, but now it's like pretty organised, that's a good thing. I usually, well, people pray for the Muslim Umma (Muslim nation), people around the world, for peace, that's the most important thing right now."
Saudi government officials say they have done all they can to ensure an orderly proceeding.
Major General Mansour al-Turki, from the Saudi Interior Ministry, says the responsibility is now on the pilgrims to comply with health and safety procedures.
"Everything is considered, everything is prepared. We have our plans, we have people trained to enforce those plans, but this cannot be done only by infrastructure and by what we do."
The five-day pilgrimage is expected to end on Sunday.
