How did the defensive army work.

All the castles had a military detachment. This military army was made up out of soldiers, archers, cavalry, and knights. This detachment protected the people in the kingdom and surrounding villages. The soldiers lived inside a guarded motte. These armies weren't big because they would need to be fead, given cloths and a home. Also they wouldn't be able to have a big army because it wouldn't fit in a kingdom full of people.