A curious superstition precipitated an outbreak, In the time of Henry I some Norman had fabricated the so-called prophecies of Merlin, which were designed to reconcile the Welsh to the Norman Conquest.  Henry was designated in them as the lion of justice, and it was given as a sign of his reign that the symbol of commerce would be split and the half be round.  The prophecy had already been fulfilled by the regulation for breaking coin at the mint, and making the half-penny a round piece by itself.  In 1279 Edward issued the farthing as an entire coin.  The change recalled the memory of Merlin’s prophecy; and the vague oracles, that had been compiled to describe Henry’s dominion over the Saxons, were easily interpreted to mean that a Welsh prince should be crowned at London, and retrieve what its natives regarded as the lost dominion of the principality.

Llewelyn, it is said, consulted a witch, who assured him that he should ride crowned through Westcheap.  But the Prince of Wales also relied on less visionary assurances.  The “quo-warranto” commission was prosecuting its labors vigorously, and had produced a widespread discontent in England, where men said openly that the King would not suffer them to reap their own corn or mow their grass.  Llewelyn was in correspondence with the malcontents, and received promises of support.  His brother David was easily induced to join the rebellion, and began it on Palm Sunday, 1282, by storming the castle of Hawarden, and making Roger de Clifford, its lord and Edward’s sheriff, his prisoner.  Flint and Rhuddlan were next reduced, and the Welsh spread over the marches, waging a war of singular ferocity, slaying, and even burning, young and old women and sick people in the villages.  The rebellion found Edward unprepared, but he met it with equal vigor and efficiency.  Making Shrewsbury his head-quarters, and moving the exchequer and king’s bench to it, he summoned troops not only from all England, but from Gascony.

It is possible that the foreign recruits were intended to strengthen the King’s hands against subjects of doubtful fidelity, but no real embarrassment from the disaffected was sustained.  The troops mustered operated in two armies, which started from Rhuddlan and Worcester, and enclosed Llewelyn, as before, from north and south.  Meanwhile the ships of the Cinque Ports reduced Anglesey, “the noblest feather in Llewelyn’s wing,” as Edward joyfully observed.  But the King was faithful to his old policy of a blockade.  A bridge of ships was thrown across the Menai Straits, and the forests between Wales proper and the English border were hewn down by an army of pioneers.  The King’s banner, the golden dragon, showed that quarter would be given.