They say you should expect the unexpected when you set off for the Hajj.
And nothing could have been more unexpected than an almighty thunderstorm on the plains of Arafat on Saturday afternoon.
Spending time praying at Arafat is the climax of the Hajj – or pilgrimage – centred on the Saudi Arabian city of Mecca.
Thunder and lightning struck just before the heavens opened – drenching almost four million pilgrims who were in the middle of intensive prayers.
None of the organisers could remember a drop of rain falling in the 20 years they had been bringing pilgrims.
Much has changed though since I was last here 15 years ago.
Back then, we stood in 45C (113F) heat under nothing more than a piece of cloth, looking across the bare desert.
Now, the Hajj is designed to fit your budget.
My group of British pilgrims were housed in air-conditioned tents with cushions for comfort and, crucially, Western-style clean toilets.
Market forces are playing an increasing part in the kind of experience you want – a five-star Hajj or a one-star Hajj.
That is not to take away from the sincerity of the faith of the pilgrims who are coming in increasing numbers. How they manage the safety of visitors and ensuring they fulfil their obligations will be crucial.
And it has to be said the country has learnt from mistakes of the past.
Hundreds used to die – mostly at the site where pilgrims stone the pillars depicting the devil, known as the Jamarat. Now a huge infrastructure has been built to cope with the numbers.
Imagine trying to move a city nearly twice the size of Birmingham overnight to Arafat, then move them all after sunset to a place called Muzdalifa, a barren landscape where they must spend the night, before returning to the tented city of Mina.
The Saudis have built a mammoth metro line to transport just some of the people. It has just three stops – Mina, Muzdalifa and Arafat – and is only open seven days a year.
It supports thousands of buses all travelling in the same direction with their millions of passengers.
The military is also out in force. The soldiers appear well trained and organised in carrying out their crowd control tasks with a duty of care, even spraying the crowds with water to keep them cool.
The Saudis want to increase the number of Hajis – pilgrims – to 10 million by 2030.
There will need to be some very cool heads to keep them all on the move and under control.