Knights, as part of the warrior class, were responsible for defending both the land and those who lived upon it from foreign invaders. Knights were the military retainers of the ruling nobiles or lords, and their services were used by the lord as he saw fit. There were two levels of knights in this period, and these levels were defined by the ownership of land, where ".some were landless household knights, while others occupied alods rather than fiefs and thus owed no feudal service". These knights held a position in society which was above that of a peasant, but certainly below the ruling aristocracy.
As mentioned, knights were paid for their services. Payment was usually land in the form of a fief, but as time passed money became the prominent way of procuring knightly service. The term of this service usually ranged from forty days to on year. According to Graham A. Loud.
Military obligations in Anglo-Saxon England had ultimately rested on possession of land. What the Norman Conquest did was to replace a relatively uniform system of military obligation, based on one man serving for every five hides worth of land, with a series of arbitrary arrangements between the king and his tenants-in-chief (nobles who held fiefs directly from the king).
The lord would come to an agreement with the king, from whom he received his land, concerning the number of knights that he would pledge to the kings service. These agreements changed constantly due to the fact that the lords of the land were always changing as well. At times when heirs failed and the lord had only daughters to succeed him, then the fief changed hands and a new arrangement over knight service had to be negotiated. There is evidence that, in the eleventh century, after a knights forty days of unpaid service ran out, the knights might have received pay for continual services. This introduction of a financial element had the effect of belittling the value of the knight by placing the emphasis on the knight's fee.