What military duties did William I’s tenants in chief owe him?

Under the feudal system established by William I, tenants in chief held their land directly from the king in exchange for specific obligations. Their primary duty was to provide military service, which included the following requirements:1

• Supply of Knights: Tenants in chief were obligated to provide a set number of knights for the royal feudal host. This quota was not necessarily determined by the size or quality of the land they held.1
• Homage and Fealty: Tenants were required to swear homage and fealty to the king as a formal recognition of their tenure and loyalty.1
• Service Limitations: While tenants initially supplied knights from their own households, they eventually granted portions of their land to knights who served them in turn. However, they were strictly forbidden from using these knights for private warfare, a practice that was prohibited in England under William I.1

In addition to these military duties, the knight service typically involved a standard period of service, often 40 days per year, during which the tenants or their knights would participate in wars, expeditions, or guard duties.2