Thousands upon thousands of hopefuls queue up, drawn by the dreams of making in big and by the drive deep within the heart that makes almost every single one of them assert (usually through tears) that 'I really, really want this more than anything, I really really want it.'
In 1095, Pope Urban gave an electrifying speech at Clermont in Central France, calling for armed men to join an expedition to save the Byzantine Empire which was teetering on the point of collapse (I have written a book about this). As word spread around Europe that something was going to be done to save Constantinople, the most important city in Europe with treasuries filled with Christianity's crown jewels, and better still, then carry on to Jerusalem, young men - and women - clamoured to take part.
But think of the rewards in the next life - that was the priests' favourite line. Sure. But also think of the glory, said the vaguer, medieval public school types; think of the financial rewards, thought the sharper ones on the make; think of what fun it will be, friends will have cajoled each other; think of what people will say if you don't go (a few of the sterner fathers would have tried that); and remember, darling, with thousands taking part, it will never be safer (the common sense of the mother, I suspect).
Unscrambling those is not easy, despite the solemn and dry explanations set out most historians of this period, who talk religious conviction, faith and endless variations of similar noble causes. Where's the fun, guys - and where's real life?
What about the peer pressure; where's the one drink too many, of course I'm coming promise that turns into something serious. Where's the showing off to the foxy daughter of the local landowner who's bound to be impressed? Where's the reluctant knight who had other things he was planning to do; or the one whose eyesight just wasn't that great and who didn't fancy it?
Well, look no further than X Factor for the perfect modern counter-sample. What anyone who watches can tell you, no two people are the same. While it's normally easy to tell a good 'un from a bad 'un, sometimes you get a surprise. But what's most striking is how many people come, year after year, to take part and to audition.
For those who go on to the live shows - woohoo ! - and reach the final stages attain a level of fame claimed by those who returned from the Holy Land after the capture of Jerusalem in 1099. The Crusaders were feted and mobbed as One Direction are today; there were signings, portraits, songs - you name it - when they got home.
That, of course, is what the Simon Cowells of the day wanted you to believe. The medieval monks who wrote the histories of the Crusade and of this period were PR men par excellence. No superyachts, fast cars and messy relationships for them (erm...); but just like with the evil genius behind X Factor, the cash flowed in. All those cathedrals where you went if you wanted to hear real singing weren't free, you know.