 Others are to be found in the formularies, many of which appeared unofficially in the Middle Ages, similar in kind to the ancient official "Liber Diurnus" of the papal chancery in use as late as the time of Gregory VII.The papal letters were forwarded by the papal officials, above all by the Apostolic Chancery, for whose use the chancery rules, "regulae cancellariae Apostolicae", were drawn up with regard to the execution and dispatch of the papal letters, dating back to the twelfth century.Nevertheless, the forging of papal letters was even more frequent in the Middle Ages than in the early Church.