The barons, however, of William I or Henry II had been a large class of comparatively small men, while the peers of Richard II were a small class of big men. The mass of lesser barons had been separated from the greater barons, and had been merged in the landed gentry who were represented by the knights of the shire in the House of Commons. The greater barons were summoned by special and individual writs to the House of Lords; but there was nothing to fetter the crown in its issue of these writs. The fact that a great baron was summoned once, did not mean that he need be summoned again, and the summons of the father did not involve the summons of his eldest son and successor. But gradually the greater barons made this summons hereditary and robbed the crown of all discretion in the matter, though it was not till the reign of Charles I that the House of Lords decided in its own favour the question whether the crown had the power to refuse a writ of summons to a peer who had once received one. With this narrowing of the baronage, the barons lost the position they had held in the thirteenth century as leaders of constitutional reform, and this part was played in the fourteenth century by the knights of the shire. The greater barons devoted themselves rather to family than to national politics; and a system of breeding-in amalgamated many small houses into a few great ones. Thomas of Lancaster held five earldoms; he was the rival of Edward II, and might well be called a peer of the crown. Edward III, perceiving the menace of these great houses to the crown, tried to capture them in its interests by means of marriages between his sons and great heiresses. The Black Prince married the daughter of the Earl of Kent; Lionel became Earl of Ulster in the right of his wife; John of Gaunt married the heiress of Lancaster and became Duke of Lancaster; Thomas of Woodstock married the heiress of the Bohuns, Earls of Essex and of Hereford; the descendants of Edmund, Duke of York, absorbed the great rival house of Mortimer; and other great houses were brought within the royal family circle. New titles were imported from abroad to emphasize the new dignity of the greater barons. Hitherto there had been barons only, and a few earls whose dignity was an office; now by Edward III and Richard II there were added dukes, marquises, and viscounts, and England might boast of a peerage nearly, if not quite, as dangerous to the crown as that of France. For Edward's policy failed: instead of securing the great houses in the interests of the crown, it degraded the crown to the arena of peerage rivalries, and ultimately made it the prize of noble factions.