The Conqueror divided the lay lands of England among his followers, to be held by the service of a fixed number of knights in his host, and imposed the same service on most of the great ecclesiastical bodies which retained their landed endowments. No record evidence exists of this action on his part, and the quota of knight-service exacted was not determined by the area or value of the lands granted (or retained), but was based upon the unit of the feudal host, the constabularia of ten knights. Of the tenants-in-chief or barons (i.e. those nobles who held fiefs directly of the crown), the principal were called on to find one or more of these units, while of the lesser ones some were called on for five knights, that is, half a constabularia.
The same system was adopted in Ireland when that country was conquered under Henry II. The baron who had been enfeoffed by his sovereign on these terms could provide the knights required either by hiring them for pay or, more conveniently when wealth was mainly represented by land, by a process of subenfeoffment, analogous to that by which he himself had been enfeoffed. That is to say, he could assign to an under-tenant a certain portion of his fief to be held by the service of finding one or more knights. The land so held would then be described as consisting of one or more knights fees, but the knights fee had not, as was formerly supposed, any fixed area. This process could be carried farther till there was a chain of mesne lords between the tenant-in-chief and the actual holder of the land; but the liability for performance of the knight-service was always carefully defined.
The primary obligation incumbent on every knight was service in the field, when called upon, for forty days a year, with specified armour and arms. There was, however, a standing dispute as to whether he could be called upon to perform this service outside the realm, nor was the question of his expenses free from difficulty. In addition to this primary duty he had, in numerous cases at least, to perform that of castle ward at his lords chief castle for a fixed number of days in the year. On certain baronies also was incumbent the duty of providing knights for the guard of royal castles, such as Windsor, Rockingham and Dover. Under the feudal system the tenant by knight-service had also the same pecuniary obligations to his lord as had his lord to the king. These consisted of:
The chief sources of information for the extent and development of knight-service are the returns (cartae) of the barons (i.e. the tenants-in-chief) in 1166, informing the king, at his request, of the names of their tenants by knight-service with the number of fees they held, supplemented by the payments for scutage recorded on the pipe rolls, by the later returns printed in the Testa de Nevill, and by the still later ones collected in Feudal Aids.
In the returns made in 1166 some of the barons appear as having enfeoffed more and some less than the number of knights they had to find. In the latter case they described the balance as being chargeable on their demesne, that is, on the portion of their fief which remained in their own hands. These returns further prove that lands had already been granted for the service of a fraction of a knight, such service being in practice already commuted for a proportionate money payment; and they show that the total number of knights with which land held by military service was charged was not, as was formerly supposed, sixty thousand, but, probably, somewhere between five and six thousand. Similar returns were made for Normandy, and are valuable for the light they throw on its system of knightservice.
The disintegration of the system was carried farther in the latter half of the 13th century as a consequence of changes in warfare, which were increasing the importance of foot soldiers and making the service of a knight for forty days of less value to the king. The barons, instead of paying scutage, compounded for their service by the payment of lump sums, and, by a process which is still obscure, the nominal quotas of knight-service due from each had, by the time of Edward I, been largely reduced. The knight's fee, however, remained a knight's fee, and the pecuniary incidents of military tenure, especially wardship, marriage, and fines on alienation, long continued to be a source of revenue to the crown. But at the Restoration (1660) tenure by knight-service was abolished by law (12 Car. II. c. 24), and with it these vexatious exactions were abolished.
The returns of 1166 are preserved in the Liber Niger (13th cent.), edited by Hearne, and the Liber Rubeus or Red Book of the Exchequer (13 cent), edited by H Hall for the Rolls Series in 1896. The later returns are in Testa de Nevill (Record Commission, 1807) and in the Record Office volumes of Feudal Aids, arranged under counties.
For the financial side of knight-service the early pipe rolls have been printed by the Record Commission and the Pipe Roll Society, and abstracts of later ones will be found in The Red Book of the Exchequer, which may be studied on the whole question; but the editors view must be received with caution and checked by JH Round's Studies on the Red Book of the Exchequer (for private circulation). The Baronia Anglica of Madox may also be consulted.
The existing theory on knight-service was enunciated by Mr Round in English Historical Review, vi., vii, and reissued by him in his Feudal England (1895). It is accepted by Pollock and Maitland (History of English Law), who discuss the question at length; by Mr JF Baldwin in his Scutage and Knight-service in England (University of Chicago Press, 1897), a valuable monograph with bibliography; and by Petit-Dutaillis, in his Studies supplementary to Stubbs' Constitutional History (Manchester University Series, 1908).