The chief business of parliament was to complete the settlement of the country. Simon won a new triumph in making terms with the king's son. Edward had witnessed the failure of his mother's attempts at invasion, the futility of the legatine anathema, and the collapse of the marchers at Worcester. He saw it was useless to hold out any longer, and unwillingly bought his freedom at the high price that Simon exacted. He transferred to his uncle the earldom of Chester, including all the lands in Wales that might still be regarded as appertaining to it. This measure put Simon in that strong position as regards Wales and the west which Edward had enjoyed since the days of his marriage. It involved a breach in the alliance between Edward and the marchers, and the subjection of the most dangerous district of the kingdom to Simon's personal authority. It was safe to set free the king's son, when his territorial position and his political alliances were thus weakened.
At the moment of his apparent triumph, Montfort's authority began to decline. It was something to have the commons on his side: but the magnates were still the greatest power in England, and in pressing his own policy to the uttermost, Simon had fatally alienated the few great lords who still adhered to him. There was a fierce quarrel in parliament between Leicester and the shifty Robert Ferrars, Earl of Derby. For the moment Leicester prevailed, and Derby was stripped of his lands and was thrown into prison. But his fate was a warning to others, and the settlement between Montfort and Edward aroused the suspicions of the Earl of Gloucester. Gilbert of Clare was now old enough to think for himself, and his close personal devotion to Montfort could not blind him to the antagonism of interests between himself and his friend. He was gallant, strenuous, and high-minded, but quarrelsome, proud, and unruly, and his strong character was balanced by very ordinary ability. His outlook was limited, and his ideals were those of his class; such a man could neither understand nor sympathise with the broader vision and wider designs of Leicester. Moreover, with all Simon's greatness, there was in him a fierce masterfulness and an inordinate ambition which made co-operation with him excessively difficult for all such as were not disposed to stand to him in the relation of disciple to master. And behind the earl were his self-seeking and turbulent sons, set upon building up a family interest that stood directly in the way of the magnates' claim to control the state. Thus personal rivalries and political antagonisms combined to lead Earl Gilbert on in the same course that his father, Earl Richard, had traversed. The closest ally of Leicester became his bitterest rival. The victorious party split up in 1265, as it had split up in 1263. And the dissolution of the dominant faction once more gave Edward a better chance of regaining the upper hand than was to be hoped for from foreign mercenaries and from papal support.
Gloucester was the natural leader of the lords of the Welsh march. He was not only the hereditary lord of Glamorgan, but had received the custody of William of Valence's forfeited palatinate of Pembroke. He had shown self-control in separating himself so long from the marcher policy; and his growing suspicion of the Montforts threw him back into his natural alliance with them. Even after the treaty of Worcester, the marchers remained under arms. They had obtained from the weakness of the government repeated prolongations of the period fixed for their withdrawal into Ireland. It was soon rumoured that they were sure of a refuge in Gloucester's Welsh estates, and Leicester, never afraid of making enemies, bitterly reproached Earl Gilbert with receiving the fugitives into his lands. Shortly after the breaking up of parliament, Gloucester fled to the march, and a little later William of Valence and Earl Warenne landed in Pembrokeshire with a small force of men-at-arms and crossbowmen. There was no longer any hope of carrying out the Provisions of Worcester, and once more Montfort was forced to proceed to the west to put down rebellion.
By the end of April Montfort was at Gloucester, accompanied by the king and Edward, who, despite his submission, remained virtually a prisoner. Earl Gilbert was master of all South Wales, and closely watched his rival's movements from the neighbouring Forest of Dean. It was with difficulty that Earl Simon and his royal captives advanced from Gloucester to Hereford, but Earl Gilbert preferred to negotiate rather than to push matters to extremities. He went in person to Hereford and renewed his homage to the king. Arbitrators were appointed to settle the disputes between the two earls, and a proclamation was issued declaring that the rumour of dissension between them was "vain, lying, and fraudulently invented". For the next few days harmony seemed restored.
Gloucester's submission lured Leicester into relaxing his precautions. His enemies took advantage of his remissness to hatch an audacious plot which soon enabled them to renew the struggle under more favourable conditions. Since his nominal release, Edward had been allowed the diversions of riding and hunting, and on May 28 he was suffered to go out for a ride under negligent or corrupt guard. Once well away from Hereford, the king's son fled from his lax custodians and joined Roger Mortimer, who was waiting for him in a neighbouring wood. On the next day he was safe behind the walls of Mortimer's castle of Wigmore, and, the day after, met Earl Gilbert at Ludlow, where he promised to uphold the charters and expel the foreigners. Valence and Warenne hurried from Pembrokeshire and made common cause with Edward and Gilbert. Edward then took the lead in the councils of the marchers, who, from that moment, obtained a unity of purpose and policy that they had hitherto lacked. He and his allies could claim to be the true champions of the Charters and the Provisions of Oxford against the grasping foreigner who strove to rule over king and barons alike.
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 of relief which his son Simon had slowly levied in the south and midlands. But his quarrel with Gloucester and his alliance with the Welsh had done much to undermine Montfort's popularity, and the younger Simon had no appreciation of the necessity for decisive action. Summoned from the long siege of Pevensey by his father's danger, he wasted time in plundering the lands of the royalists, and only left London on July 8, whence he led his men by slow stages to Kenilworth. On July 31 young Simon's troops took up their quarters for the night in the open country round Kenilworth castle. They had no notion that the enemy was at hand and troubled neither to defend themselves nor to keep watch. Edward, warned by spies of their approach, abandoned his close guard of the Severn fords, and in the early morning of August 1 fell suddenly upon the sleeping host and scattered it with little difficulty. The younger Simon and a few of his followers took refuge in the castle. As a fighting force the army of relief ceased to exist.
Leicester, knowing nothing of his son's disaster, made his way, on August 3, from Kempsey to Evesham, where he rested for the night. Next morning, after mass and breakfast, the army was about to continue its march, when scouts descried troops advancing upon the town. At first it was hoped that they were the followers of young Simon, but their near approach revealed them to be the army of the marchers. With extraordinary rapidity Edward led his troops back to Worcester as soon as he had won the fight at Kenilworth. Learning there that Simon had crossed the river in his absence, he at once turned back to meet him, seeking to elude his vigilance by a long night march by circuitous routes. The result was that for the second time he caught his enemy in a trap.
Evesham, like Lewes, stands on a peninsula. It is situated on the right bank of a wide curve of the Avon, and approachable only by crossing over the river, or by way of the sort of isthmus between the two bends of the Avon a little to the north of the town. Edward occupied this isthmus with his best troops, and thus cut off all prospect of escape by land. The other means of exit from the town was over the bridge which connects it with its south-eastern suburb of Bengeworth, on the left bank of the river. Edward, however, took the precaution to detach Gloucester with a strong force to hold Bengeworth, and thus prevent Simon's escape over the bridge. The weary and war-worn host of Montfort, then, was out-generalled in such fashion that effective resistance to a superior force, flushed by recent victory, was impossible. Simon himself saw that his last hour was come; yet he could not but admire the skilful plan which had so easily discomfited him. "By the arm of St. James," he declared, "they come on cunningly. Yet they have not taught themselves that order of battle; they have learnt it from me. God have mercy upon our souls, for our bodies are theirs."