On the death of that monarch, in the midst of a civil war and a foreign invasion, he assembled the loyal bishops and barons of the land at Gloucester, and by his eloquence, talents, and address, secured the throne for king John's son, the young prince Henry.[511] The greater part of England was at that time in the possession of prince Louis, the dauphin of France, who had landed with a French army at Sandwich, and was supported by the late king's rebellious barons in a claim to the throne. Pembroke was chosen guardian and protector of the young king and of the kingdom, and exerted himself with great zeal and success in driving out the French, and in bringing back the English to their antient allegiance.[512] He offered pardon in the king's name to the disaffected barons for their past offences. He confirmed, in the name of the youthful sovereign, MAGNA CHARTA and the CHARTA FORESTÆ; and as the great seal had been lost by king John, together with all his treasure, in the washes of Lincolnshire, the deeds of confirmation were sealed with the seal of the earl marshall.[513] He also extended the benefit of Magna Charta to Ireland, and commanded all the sheriffs to read it publicly at the county courts, and enforce its observance in every particular. Having thus exerted himself to remove the just complaints of the disaffected, he levied a considerable army, and having left the young king at Bristol, he proceeded to lay siege to the castle of Mountsorel in Leicestershire, which was in the possession of the French. Prince Louis had, in the mean time, despatched an army of twenty thousand men, officered by six hundred knights, from London against the northern counties. These mercenaries stormed various strong castles, despoiled the towns, villages, and religious houses, and laid waste the open country. The protector concentrated all his forces at Newarke, and on Whit-monday, A. D. 1217, he marched at their head, accompanied by his eldest son and the young king, to raise the siege of Lincoln Castle. On arriving at Stow he halted his army, and leaving the youthful monarch and the royal family at that place under the protection of a strong guard, he proceeded with the remainder of his forces to Lincoln. On Saturday in Whitsun week (A. D. 1217) he gained a complete victory over the disaffected English and their French allies, and gave a deathblow to the hopes and prospects of the dauphin. Four earls, eleven barons, and four hundred knights, were taken prisoners, besides common soldiers innumerable. The earl of Perch, a Frenchman, was slain whilst manfully defending himself in a churchyard, having previously had his horse killed under him. The rebel force lost all their baggage, provisions, treasure, and the spoil which they had accumulated from the plunder of the northern provinces, among which were many valuable gold and silver vessels torn from the churches and the monasteries.