Patrol is an action that can be carried out by commanders and their units, which has them search the province for stealthy units and quell unrest in the province. Additionally, for provinces with a fort, only patrolling forces will be involved in any battles in the province outside the fort, along with any province defence. Troops moving to a forted province may join the patrollers for battles by clicking their "move" order and selecting "move and patrol".

Note that each unit has a calculated patrol strength, derived from its attributes. This value is relevant to the discussions below, and is given by:

(precision + map move)/20, where map move = 30 if the unit is flying

Undisciplined units suffer a flat -0.5 to this value, which can reduce their patrol strength below zero. This means that they actively hinder patrolling efforts in the province. This value appears to be doubled for commanders. Additionally, this value is modified by the patrol bonus ability. Clicking the precision stat on the unit stat panel will display this value, however it appears to be always rounded up to one decimal place. There is limited evidence to suggest that the game does in fact use the unrounded values for calculations. The active patrol strength of a province appears to simply be the sum of this value for all patrolling units, plus the values produced from province defence.

Stealthy units may be discovered by patrolling forces. If a unit is invisible, it can only be detected by patrollers with spirit sight. The mathematical description for this process is as follows:

Stealth strength = (Leader's stealth ability) - (number of stealthy units under their command with stealth ability < 50)

Destealth strength = (Sum of patrolling units' patrol strengths) - min(unrest, 100)/2 + max(0, province defence - 14)

Sneaking units are discovered if:

Destealth + 2d25 > Stealth + 2d25

Both of these rolls are open-ended.

When patrolling a province with unrest, the turn report will include some number of filthy brigands that were found. This number is the points of unrest reduced by the patrolling action. Experimentally, patrolling appears to reduce province population by about 2.5 per point of unrest removed (or filthy brigand) removed in this way.

The points of unrest reduced appears to be poorly understood, however it appears to be incapable of exceeding the total patrol strength in the province. It is this observation which has produced results suggesting that the game does in fact use unrounded patrol strength values for carrying out its calculations.