Has a Patrol button in the GUI. Once put on a patrol route, entity(s) repeatedly moves from one extreme limit back to the other, back and forth. There is no limit to the number of Patrol routes that may be set up.
(Action: Activate the Patrol command through GUI, then right-click unoccupied terrain to set up patrol path between entity's current position and this location; hold down Shift and right-click additional positions to establish more waypoints in the circular patrol path.)
Simon asked for further clarification about the waypoint path, so here's a couple of screenshots to clarify the situation ...
<Actions> <Patrol /> </Actions>