The Fort is responsible for recruiting and housing your city garrison. Providing a supply of weapons is available in the warehouse, troops will contstantly be created in that fort until all three barracks are full. You may have a total of three forts per city. For more information on soldiers, see this page.
Cost: 1000 Denarii
The javelin maker will supply you with a supply of javelins for troops, but a supply of wood is needed in the warehouse first.
Cost: 300 Denarii
The fire watch will put out any fires near your city, but a well must be placed as this is where the water supply comes from.
Cost: 200 Denarii
This will allow people to get in and out of the city walls.
Cost: 100 Denarii