but Henry's further influence was restricted by poor health and blindness for the last fifteen years of his life. Succession Henry's son, also called Henry, was born at the castle of Grosmont in Monmouthshire between 1299 and 1314. According to the younger Henry's memoirs, he was better at martial arts than academic subjects and did not learn to read until later in life. Henry was coeval with Edward III and was pivotal to his reign, becoming his best friend and most trusted commander. Henry was knighted in 1330, represented his father in parliament and fought in Edward's Scottish campaign. After the outbreak of the Hundred Years' War, Henry took part in several diplomatic missions and minor campaigns and was present at the great English victory in the naval Battle of Sluys in 1340. Later, he was required to commit himself as hostage in the Low Countries for Edward's considerable debts. He remained hostage for a year and had to pay a large ransom for his own release. In 1345, Edward III launched a major, three-pronged attack on France. The Earl of Northampton attacked from Brittany, Edward from Flanders, and Henry from Aquitaine in the south. Moving rapidly through the country, Henry confronted the Comte d'Isle at the Battle of Auberoche and achieved a victory described as "the greatest single achievement of Lancaster's entire military career". The ransom from the prisoners has been estimated at £50,000. Edward rewarded Henry by including him as a founding knight of the Order of the Garter. An even greater honour was bestowed on Lancaster when Edward created him Duke of Lancaster. The title of duke was relatively new in England, with only Cornwall being a previous ducal title. Lancaster was also given palatinate status for the county of Lancashire, which entailed a separate administration independent of the crown. There were two other counties palatine; Durham was an ancient ecclesiastical palatinate and Chester was crown property. Earls of Lancaster | Edmund Crouchback, 1st Earl of Lancaster and Leicester || || 16 January 1245Londonson of Henry III of England and Eleanor of Provence|| (1) Aveline de Forz12690 children(2) Blanche of Artois21 September 12714 childrenThomas, 2nd Earl of LancasterHenry, 3rd Earl of LancasterJohn of Lancaster, Lord of BeaufortMary of Lancaster||5 June 1296Bayonne, Gasconyaged 51 |- | Thomas, 2nd Earl of Lancaster and Leicester|| || 1278Grismond Castle, Monmouthshireson of Edmund Crouchback and Blanche of Artois || Alice de Lacy,