A manuscript found at Bamberg states that Irish visitors to the court of Merfyn Frych ap Gwriad (died 844), king of Gwynedd in Wales were given a cryptogram which could only be solved by transposing the letters from Latin into Greek.
His father Merfyn Frych ap Gwriad had seized the throne of Gwynedd on the death of the last of the old royal line Hywel ap Rhodri Molwynog.