Montfort’s small force was cut off from its base by the rapidity of the marchers’ movements.  It was in vain that all the supporters of the existing government were summoned to the assistance of the hard-pressed army at Hereford.  Before the end of June, Edward completed the conquest of the Severn valley by the capture of the town and castle of Gloucester.  A broad river and a strong army stood between Montfort and succour from England.  Leicester then turned to Llewelyn of Wales, who took up his quarters at Pipton, near Hay.  There, on June 22, a treaty was signed between the Welsh prince and the English king by which Henry was forced to make huge concessions to Llewelyn in order to secure his alliance.  Llewelyn was recognised as prince of all Wales.  The overlordship over all the barons of Wales was granted to him, and the numerous conquests, which he had made at the expense of the marchers, were ceded to him in full possession.

Thus Llewelyn, like his grandfather in the days of the Great Charter, profited by the dissensions of the English to obtain the recognition of his claims which had invariably been refused when England was united.  The Welsh prince gained a unique opportunity of making his weight felt in general English politics, but with all his ability he hardly rose to the occasion.  Montfort had pressing need of his help.  A few days after the treaty of Pipton, Gloucester Castle opened its gates to Edward, and the marchers advanced westwards to seek out Earl Simon at Hereford.  Leicester fled in alarm before their overwhelming forces.  He was driven from the Wye to the Usk, and, beaten in a sharp fight on Newport bridge, found refuge only by retreating up the Usk valley, whence he escaped northwards into the hilly region where Llewelyn ruled over the lands once dominated by the Mortimers.  Before long Montfort’s English followers grew weary of the hard conditions of mountain warfare.  With their heavy armour and barbed horses it was difficult for them to emulate the tactics of the Welsh, and they revolted against the simple diet of milk and meat that contented their Celtic allies.  They could not get on without bread, and, as bread was not to be found among the hills, they forced their leader to return to the richer regions of the east.  Llewelyn did little to help them in their need, and did not accompany them in their march back to the Severn valley, though a large but disorderly force of Welsh infantry still remained with Simon as the fruit of the alliance with their prince.

By the end of July, Simon was once more in the Severn valley, seeking for a passage over the river.  On August 2 he found a ford over the stream some miles south of Worcester.  There he crossed with all his forces and encamped for the night at Kempsey, one of Bishop Cantilupe’s manors on the left bank.  His skill as a general had extricated him from a position of the utmost peril.  All might yet be regained if he could join forces with an army