Merfyn claimed descent from Llywarch Hen through him, and the royal pedigree in Jesus College MS. 20 says that Gwriad was the son of Elidyr, who bears the same name as his ancestor, the father of Llywarch Hen, Elidyr lydanwyn.
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King Beornwulf was killed fighting the East Anglians in 826, his successor Ludeca suffered the same fate the following year, and Mercia was conquered and occupied by Ecgberht of Wessex in 829.
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It was discovered at Bamberg, Germany and it contains characters that must be translated from Greek numerals to Latin text using a key in order to read the message (a form of cryptogram), hence the document's name.
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Coastal Wales along the Dee Estuary must have remained under Mercia through 821, as Coenwulf is recorded dying peacefully at Basingwerk in that year.