Here is the meaning of the word, PATROL

Patrol ( v. ) - t To go the rounds of, as a sentry, guard, or policeman; as, to patrol a frontier; to patrol a beat.
Patrol ( v. i. ) - A going of the rounds along the chain of sentinels and between the posts, by a guard, usually consisting of three or four men, to insure greater security from attacks on the outposts.
Patrol ( v. i. ) - A movement, by a small body of troops beyond the line of outposts, to explore the country and gain intelligence of the enemy's whereabouts.
Patrol ( v. i. ) - Any perambulation of a particular line or district to guard it; also, the men thus guarding; as, a customs patrol; a fire patrol.
Patrol ( v. i. ) - The guard or men who go the rounds for observation; a detachment whose duty it is to patrol.
Patrol ( v. i. ) - To go the rounds along a chain of sentinels; to traverse a police district or beat.