The Beaufort children, three sons and a daughter, were legitimised by royal and papal decrees after John and Katherine married. A later proviso that they were specifically barred from inheriting the throne—the phrase "" ("except royal status")—was inserted with dubious authority by their half-brother Henry IV. John died of natural causes on 3 February 1399 at Leicester Castle, with his third wife Katherine by his side. Because of his rank, John of Gaunt was one of England's principal military commanders in the 1370s and 1380s, though his enterprises were never rewarded with the kind of dazzling success that had made his elder brother Edward the Black Prince such a charismatic war leader. On the resumption of war with France in 1369, John was sent to Calais with the Earl of Hereford and a small English army with which he raided into northern France. On 23 August, he was confronted by a much larger French army under Philip the Bold, Duke of Burgundy. Exercising his first command, John dared not attack such a superior force and the two armies faced each other across a marsh for several weeks until the English were reinforced by the Earl of Warwick, at which the French withdrew without offering battle. John and Warwick then decided to strike Harfleur, the base of the French fleet on the Seine. Further reinforced by German mercenaries, they marched on Harfleur, but were delayed by French guerilla operations while the town prepared for a siege. John invested the town for four days in October, but he was losing so many men to dysentery and bubonic plague that he decided to abandon the siege and return to Calais. During this retreat, the army had to fight its way across the Somme at the ford of Blanchetaque against a French army led by Hugh de Châtillon, who was captured and sold to Edward III. By the middle of November, the survivors of the sickly army returned to Calais, where the Earl of Warwick died of plague. Though it seemed an inglorious conclusion to the campaign, John had forced the French king, Charles V, to abandon his plans to invade England that autumn. In the summer of 1370, John was sent with a small army to Aquitaine to reinforce his ailing elder brother, the Black Prince, and his younger brother Edmund of Langley, Earl of Cambridge. With them, he participated in the Siege of Limoges (September 1370). He took charge of the siege operations and at one point engaging in hand-to-hand fighting in the undermining tunnels.