in that way obtain the necessary resources for his crusade. William was as eager to get the duchy as Robert was to get the money, and a bargain was soon struck between them. William carried over to Normandy 10,000 marks--the mark was two-thirds of a pound--and received from Robert, as a pledge for the payment of the loan, the possession of the duchy for a period of at least three years, and for how much longer we cannot now determine with certainty, but for a period which was probably intended to cover Robert's absence. The duke then set off at once on his crusade, satisfied with the consciousness that he was following the plain path of duty. With him went his uncle, Odo, Bishop of Bayeux, to die in Sicily in the next winter. William had bought the possession of Normandy at a bargain, but he did not propose to pay for it at his own cost. The money which he had spent, and probably more than that, he recovered by an extraordinary tax in England, which excited the bitter complaints of the ecclesiastical writers. If we may trust our interpretation of the scanty accounts which have reached us, this money was raised in two ways, by a general land-tax and by additional personal payments from the king's own vassals. By grant of the barons of England a Danegeld of four shillings on the hide, double the usual tax, was collected, and this even from the domain lands of the Church, which it was asserted, though with doubtful truth, had always been exempt. The clergy paid this tax, but entered formal protest against it, probably in order to prevent, if possible, the establishment of a precedent against their liberties. The additional payment suggested by some of the chroniclers is to be seen in detail in the case of Anselm, who regarded this as a reasonable demand on the part of the king, and who, besides passing over to the treasury what he collected from his men, made on advice a personal payment of 200 marks, which he borrowed from the Canterbury monks on the security of one of his domain manors. Not all the churches were so fortunate as to have the ready money in the treasury, and in many cases ornaments and sacred utensils were sacrificed, while the lay lords undoubtedly recovered their payments by like personal auxilia from their men, until the second tax really rested like the first upon the land. The whole formed a burden likely to cripple seriously the primitive agriculture of the time, as we are told that it did.