The politic ruler of England had, in the completion of _Domesday Book_, possessed himself of the most perfect instrument for the profitable administration of his government. He was no longer working in the dark, whether he called out soldiers or levied taxes. He had carried through a great measure, rapidly, and with a minuteness which puts to shame some of our clumsy modern statistics. But the Conqueror did not want his books for the gratification of official curiosity. He went to work when he knew how many tenants-in-chief he could command, and how many men they could bring into the field. He instituted the great feudal principle of knight-service. His ordinance is in these words: "We command that all earls, barons, knights, sergeants, and freemen be always provided with horses and arms as they ought, and that they be always ready to perform to us their whole service, in manner as they owe it to us of right for their fees and tenements, and as we have appointed to them by the common council of our whole kingdom, and as we have granted to them in fee with right of inheritance." These words, "in fee, with right of inheritance," leave no doubt that the great vassals of the crown were absolute proprietors, and that all their subvassals had the same right of holding in perpetuity. The estate, however, reverted to the crown if the race of the original feoffee became extinct, and in cases, also, of felony and treason. When Alain of Bretagne, who commanded the rear of the army at the battle of Hastings, and who had received four hundred and forty-two manors, bowed before the King at Salisbury, at the great council in 1085, and swore to be true to him against all manner of men, he also brought with him his principal _land-sittende_ men (land-owners), who also bowed before the King and became his men. They had previously taken the oath of fealty to Alain of Bretagne, and engaged to perform all the customs and services due to him for their lands and tenements. Alain, and his men, were proprietors, but with very unequal rights. Alain, by his tenure, was bound to provide for the King as many armed horsemen as the vast extent of his estates demanded. But all those whom he had enfeoffed, or made proprietors, upon his four hundred and forty-two manors, were each bound to contribute a proportionate number. When the free service of forty days was to be enforced, the great earl had only to send round to his vassals, and the men were at his command.