A Customs House is a building that can be placed on field tiles after the Trade technology has been researched. It increases resource production by 2 Stars for each adjacent port, no matter if it was built before or after the Customs House.
It costs 5 stars to build a Customs House.
Each city may only contain one Customs House.
Note that it does not provide population like the other tier 3 "counting" buildings. Forges give you population for each Mine, Sawmills give population for each Lumber Hut, Windmills give population for each Farm, but the Customs House produces Stars instead.
- If you are planning to use Customs Houses, look for good locations before you actually place them. Keep that square free of development until you research Trade to avoid having to destroy buildings previously constructed on that tile.
- Customs Houses are useful investments during wartime, providing stars even when its city is being captured.