All these elements counted for something, but failed to restrain sufficiently even an average king; while they were powerless against a strong ruler like William I. The only moment at which the Crown might be taken at a clear disadvantage was during the interregnum which followed the death of the last occupant of the throne. Two or more rival heirs might aspire to the high position, and would be eager to make promises in return for support. Thus, William Rufus, at his father’s death, anxious to prevent his elder brother, Duke Robert, from making good his claim to the English throne, succeeded chiefly through the friendship of Lanfranc. To gain this, he was compelled to make promises of good government, and to follow his father’s precedent by taking the oath in the ancient form, in which it had been administered by Dunstan to Ethelred. In the same reign began the practice of supplementing verbal promises by sealed charters, which in some respects must be regarded simply as the old coronation oath confirmed, expanded, and reduced to writing. No such charter was indeed issued either by Rufus or by his father when they were crowned; but the younger William, at a critical period later in his reign, seems to have granted a short Charter of Liberties, the exact contents of which have not come down to us. At the death of Rufus, his younger brother, Henry I., found himself hard pressed in the competition for the English Crown by Duke Robert (the Conqueror’s eldest son). By a treaty made at Caen in 1091, Duke Robert and Rufus had agreed that each should constitute the other his heir. Thus Henry was, in a sense, a usurper, and this circumstance made it necessary for him to bid high for influential support.[165] It is to this doubtful title, coupled with the knowledge of widespread disaffection, that Englishmen owe the origin of the first Charter of Liberties that has come down to us.[166] ----- Footnote 165: Stubbs, _Const. Hist._, I. 328-9, and authorities there cited. Footnote 166: See Appendix. ----- This charter was the price paid by Henry for the support he required in his candidature for the Crown. In granting it he admitted, in a sense, the contractual basis of his kingship. In discussing its tone and general tenor there is ample room for differences of opinion. Dr. Stubbs[167] maintains that Henry thereby “definitely commits himself to the duties of a national King.” Writers of almost equal authority somewhat modify this view, holding that, although circumstances forced Henry to pose as the leader of the entire nation, yet nothing of this could be traced in the charter, the basis of which seems to have been feudal rather than national.[168] ----- Footnote 167: _Const. Hist._, I. 331. Footnote 168: See Prothero, _Simon de Montfort_, 16: “That charter had been mainly of a feudal character; it contained no provision for, and scarcely even hinted at, a constitutional form of government.” -----