There are an estimated 1.6 billion Muslims. Each is supposed to do the Hajj to Mecca.
If each lives 70 years and no more are born/converted then that is nearly 23 million pilgrims for each of those 70 years.
There is no way to have 23 million people assembled without either a stampede, massive thirst or the explosion of a critical mass of Porta-Potties.
If BwanaNdege has the math correct, and If the number of pilgrims is spread out evenly (a lot of Ifs, I know) then that comes to about 63,000 a day, which seems a manageable number. Of course that would take an impossible effort to spread out evenly.