If you've already got a Town Watch in place, your Town Hall staff will figure out that that a stationary watch may not be the best defensive plan. How about a moving patrol? Hence, the Town Patrol, which will tell your invisible watch crew to get their butts in gear. The innovation has an added bost: it boosts building LOS by another 4 tiles (in addition to the +4 already given by your watchmen).
Available to: All (Requires Town Watch)
Researched at: Town Hall
Cost: 300 Food, 200 Florins
Effect: Building LOS +4