After the Normans conquered England, the pope sanctioned them, on account of how much slaughtering had gone on.  So, being sanctioned, they were very sorry. Which is why William the Conqueror founded Battle Abbey, where the Battle of Hastings was. And when he did that, he gave the monks some special rights (mostly having to do with not being required to listen to the bishop), but they didn't get written down, because nobody needed to; the king, after all, had said so.  But time moved on, and written culture became the thing, so the monks needed a charter to prove the things William said. So they made some. About seven of them. They were very nice looking forgeries, but nobody believed them. However! There was a forgery ring running out of Winchester Abbey. Really.  You can't make this stuff up.