Indiana Jones & the Last Crusade?

hmm... that's a good point. I never thought of that after watching it for almost 14 or 15 years.

It tells you in the film, the cult were there to keep the grail safe, the bad guys wanted it to make their army unstoppable and march all over the world.

The Grail could not pass beyond the great seal as a price for immortality

The Grail itself could not pass beyond the Great seal but someone could still go in, find the grail, and drink from it giving them eternal life or I suppose someone whose goal was to destroy the grail could do so if it wasn't guarded. I guess that is the reason why there was a cult who was dedicated to protecting it too.

Because it's a movie. Don't you think the Holy Grail would be protected even if it couldn't leave the seal, someone could waltz in there and keep it for themselves if it wasn't protected, They could tell the whole world about it and it would have destroyed eveything still. But all in all, its just a moive, enjoy it for what it is.

the knights were the ones who put the seal there. maybe somebody had to stay behind to keep it working.

EDIT: no. jones father would only have been immortal if he stayed behind the great seal. that was the price you paid for immortality.