This was a document which contained a long list of promises made by King John (1199-1216) which was for the main part, clauses that gave barons more power than they already had.
However, King John did not sign the Magna Carta, as he could not write, but his royal seal was affixed to the several copies made.
He authorised this under pressure and shortly afterwards the Pope, Innocent III said he would not abide by its terms on the grounds that they extracted under pressure.