http://www.bibleinterp.com/opeds/forge357905.shtml
Taken as a whole, medieval monks and clerics were probably the most prolific forgers of all time. For centuries they controlled access to official documents, placing them in a perfect position to alter or forge those documents, should they so desire. And judging by the volume of their output, they evidently did so desire. What’s more, their superiors could be counted on to overlook, or even approve, any textual inventions that benefitted the Church.