the support of every Welsh tenant of a marcher lord, and at last grew strong enough to disregard the truces and wage open war against the marchers.  It was in vain that Edward, the greatest of the marcher lords, persuaded David, the Welsh prince’s brother, to rise in revolt against him.  Llewelyn devastated the four cantreds to the gates of Chester, and at last, after long sieges, forced the war-worn defenders of Deganwy and Diserth to surrender the two strong castles through which alone Edward had retained some hold over his Welsh lands.  It was the same in the middle march, where Llewelyn turned his arms against the Mortimers, and robbed them of their castles.  Even in the south the lord of Gwynedd carried everything before him.  “If the Welsh are not stopped,” wrote a southern marcher, “they will destroy all the lands of the king as far as the Severn and the Wye, and they ask for nothing less than the whole of Gwent.”  Up to this point the war had been a war of Welsh against English, but Montfort sought compensation for his losses in England by establishing relations with the Welsh.  The alliance between Montfort and their enemy had a large share in bringing about the secession of the marchers.  Their alliance with Edward neutralised the action of Montfort, and once more enabled Henry to repudiate the Provisions.

In the summer of 1263, Edward and Montfort both raised armies.  Leicester made himself master of Hereford, Gloucester, and Bristol, and when Edward threw himself into Windsor Castle, he occupied Isleworth, hoping to cut his enemy off from London, where the king and queen had taken refuge in the Tower.  But the hostility of the Londoners made the Tower an uneasy refuge for them.  On one occasion, when the queen attempted to make her way up the Thames in the hope of joining her son at Windsor, the citizens assailed her barge so fiercely from London Bridge that she was forced to return to the Tower.  The foul insults which the rabble poured upon his mother deeply incensed Edward and he became a bitter foe of the city for the rest of his life.  For the moment the hostility of London was decisive against Henry.  Once more the king was forced to confirm the Provisions, agree to a fresh banishment of the aliens, and restore Hugh Despenser to the justiciarship.  This was the last baronial triumph.  In a few weeks Edward again took up arms, and was joined by many of Montfort’s associates, including his cousin, Henry of Almaine.  Even the Earl of Gloucester was wavering.  The barons feared the appeal to arms, and entered into negotiations.  Neither side was strong enough to obtain mastery over the other, and a recourse to arbitration seemed the best way out of an impossible situation.  Accordingly, on December, 1263, the two parties agreed to submit the question of the validity of the Provisions to the judgment of Louis IX.