Knight-service

Knight-service was a form of Feudal land tenure under which a knight held a fief or estate of land termed a knight's fee (fee being synonymous with fief) from an overlord conditional on him as tenant performing military service for his overlord.

It is associated in its origin with that development in warfare which made the mailed horseman, armed with lance and sword, the most important factor in battle. It was long believed that knight-service was developed out of the liability, under the English system, of every five hides of land to provide one soldier in war. It is now held that, on the contrary, it was a novel system in England when it was introduced after the Conquest by the Normans, who relied essentially on their mounted knights, while the English fought on foot. It existed in Normandy where a knight held a fief termed a fief du haubert, from the hauberk or coat of mail (Latin: lorica) worn by knights. Allusion is made to this in the coronation charter of Henry I (1100), which speaks of those holding by knight-service as "milites qui per loricam terras sues deserviunt."

The Conqueror divided the lay lands of England among his magnates in the form of "honours" or great blocks of land. These were subdivided by the magnates into smaller manors and yet smaller divisions or fiefs just large enough to support one knight, termed knight's fees. The knight paid homage to his overlord by taking a vow of loyalty and accepting the obligation to perform military service for his overlord.

The same system was adopted in Ireland when that country was conquered under Henry II. The magnate who had been enfeoffed by his sovereign for his honour of land 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 subinfeudation, 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 direct military service or the service of providing a mercenary knight. The land so held would then be described as consisting of one or more knight's fees, but the knight's-fee had not any fixed area, as different soils and climates required differing acreages to produce a given profit requisite to support a knight and his entourage. This process could be carried farther till there was a chain of mesne lords between the tenant-in-chief and the actual occupier of the land. The liability for performance of the knight-service was however always carefully defined.

...
Wikipedia