I have now endeavoured to make plain one of the chief flaws in the view at present accepted, namely, that it is mainly grounded on the negative evidence of Domesday, which evidence will not bear the construction that has been placed upon it--and further that, even if it did, we should be landed in a fresh difficulty, the gulf between Domesday and Henry's charter being only to be bridged by the assumption that Ranulf Flambard 'devised' and introduced military tenure, with its results--an assumption, we have seen, which the facts of the case not only fail to support, but even discountenance wholly. Let us pass to a second difficulty. When we ask the advocates of the view I am discussing what determined the number of knights due to the crown from a tenant-in-chief, we obtain, I venture to assert, no definite answer. At times we are told that it was the number of his hides; at times that it was the value of his estate. Gneist, who has discussed the matter in detail, and on several occasions, has held throughout, broadly speaking, the same view: he maintains that 'since Alfred's time the general rule had been observed that a fully equipped man should be furnished for every five _hidæ_, but it had never been established as a rule of law as in the Carlovingian legislation':[24] consequently, he urges, 'a fixed standard for the apportionment of the soldiery was wanting' at the time of the Conquest, and this want was a serious flaw in the Anglo-Saxon polity. William resolved to make the system uniform, and the object that the royal administration now pursued for a century was to impose upon the whole mass of old and new possessors an equal obligation to do service for reward. The standard adopted in carrying out this system was approximately that of the five hides possession of the Anglo-Saxon period; yet with a stricter rating according to the value of the produce.[25] The difficulty encountered in ascertaining this value was a main cause of the Domesday Survey being undertaken. This is Gneist's special point on which he invariably insists: 'Domesday book laid the basis of a roll of the crown vassals';[26] upon it, 'in later times, the fee-rolls were framed'.[27] By its evidence, 'according to the extent and the nature of the productive property, could be computed how many shields were to be furnished by each estate, according to the gradually fixed proportion of a £20 ground rent'.[28] For 'the _feuda militum_ thus computed are no knights' fees of a limited area',[29] but 'units of possession', the unit being £20 in annual value.