Ddu o Hiraddug the encrypted message reads, HOC SI PETATUR LAPSIS ISTE CAUSA NOTATUR | EINION OXI RIRID VLAIDD FILIUS HOC MEMORATUR. A translation has been given as, THAT NEAR HERE THE CAUSE HIS FALL, IF THEY ASK OF SECRET WRITING | REMEMBER EINION, THIS IS THE SON OF RIRID VLAIDD. Description Dyserth Castle was situated in a naturally defensible strategic location on a mountain ridge at the north end of the Clwydian hills, west of the Conwy River. The small internal courtyard for the castle was entered by way of a twin-towered gatehouse. The castle had a concentric outer curtain wall and according to historian Sean Mason that would be the first constructed in Wales' castles. Dyserth Castle was the last of the British fortified defence castles on the Clwydian hill range in the Middle Ages. Demise Dyserth Castle was first attacked by the Welsh around 1245. It was attacked a number of times over nearly two decades and was seized and occupied at different periods by the English and Welsh. In 1263, it was totally destroyed by the Welsh prince Llywelyn ap Gruffudd after several weeks of a blockade and siege. During World War I, the ridge served as a quarry and much of the former castle ruins were removed. References Sources External links Croes Einion secret writing picture Castles in Denbighshire Castle ruins in Wales Scheduled monuments in Denbighshire