These are the troops that guard the fortifications in the fief and maintain order. They enforce the laws and, basically, your will. Since they are primarily composed of the knights and men at arms that live in the fief, and many are serving you part time, they don't get paid as much as mercenaries.

These payments also include payments for their weapons, equipment and, for some of them, horses. This still gives you about one full time soldier for every thousand ducats spent each season in the fief. However, these troops cannot be moved outside the fief for, in addition to being the source of law and order, they, and their families, live in the fief and the money you pay them is essentially a bribe to insure the loyalty of your best soldiers. Many of them are landowners and your vassals in the fief. It's the loyalty of this group that is most crucial to your hold on the fief.

The maximum you can spend per capita is 14 ducats per season.

Figures for troop types in fiefs (number per thousand population)