The manual (and the civilopedia) state for the harbor:

Effects: Forms a naval Trade Route with the Capital City, +25% Production of Naval Units, City must be on a coast.

It is unclear to me though whether I need a harbor in the capital to make the trade routes from other harbors work ... ?

3 Answers 3


The trade network is just that - a network.

In the same way that a city can be linked by road via another city already linked by road - they don't all need their own roads directly to the capital - your trade network will spread via harbours.

What this means is you need at least one harbour within each "sub network" of your trade network. Here is a quick diagram:

Continent A     Water     Continent B
            |~ ~ ~ ~ ~ ~|
     1------2 ~ ~ ~ ~ ~ 3------4-----5
            |~ ~ ~ ~ ~ ~|

City 1 is your capital, and linked by road to city 2. If city 2 and city 3 both have a harbour then they extend the trade route across the water, this means 4 and 5 are also connected, because they are linked to 3 and so, by proxy, use it's harbour link.

If in this example, even if 2 was your capital it would still need a harbour to extend your trade route accross the water, having a harbour in 3 alone is not sufficent.

This also works if 2 and 3 were on the same continent, but not connected by road/rail.

  • You avoid a ton of spurious warnings about broken trade networks from the game if you DON'T put a harbor in your capital! Just have the capital connect to a city that has a port by land, and then the game doesn't whine at you endlessly.
    – Mordachai
    Commented Oct 14, 2010 at 17:46

Just to explicitly emphasize a fact which is implied but not expressly stated in DMA57361's and Mad Scientist's answers: the harbour does not need to reside in one of your own cities. An allied city state or a puppet city which has built a harbour will be perfectly sufficient for as long as you have a route to it. They will grant you all their ressources, including trade connections.

With some luck, you can have your continents interconnected without paying maintenance on a single harbour yourself if you connect to friendly (or oppressed) other shore cities.

  • 1
    Now that is very interesting to know, +1 for useful facts! It seems obvious now you've said it, but I probably wouldn't have thought of using a City State's harbour in game myself.
    – DMA57361
    Commented Oct 14, 2010 at 11:56
  • 1
    +1: Interesting. I'm tending to think that maybe the trade route stuff is not as buggy as I though, just that the rules are not explained well. Commented Oct 14, 2010 at 12:09
  • 1
    Interesting...but given that a harbor costs 3 gold/turn and a tile of road costs 1 gold/turn, and that cities can't be built within 3 tiles of each other, it'll generally be cheaper in the long run to build your own harbors. (Though there are times this might work better, if you have excess worker capacity, and more important things for your production capacity than harbors). Commented Mar 18, 2012 at 10:47
  • That's true, yet it may still be worth the money. Sometimes a city state will ask you to connect to them, making them very friendly for quite some time. In case of a crowded map using a city state's harbour can also be more desirable than having to raze other cities just to make room for a poor harbour town between high mountains and deep seas.
    – Olfan
    Commented Sep 7, 2012 at 10:24

Not necessarily, you just need one harbor in a city that is already connected to the capital.

There also needs to be a discovered route between the harbors, or the connection won't work. I think also enemy units (or barbarians) can interrupt trade routes, but I'm not sure how that works exactly.

  • But, if you have only one city - the capital - on the coast and then settled a second city somewhere else - also on the coast - would both need a harbour to establish a trade route?
    – DMA57361
    Commented Oct 14, 2010 at 10:53
  • Yes, you need two harbors to create a connection, but the first harbor can be anywhere in your existing trade network. Commented Oct 14, 2010 at 11:09
  • Good point with being able to see a valid water link for harbours to work, and barbarians blocking, I'd missed those.
    – DMA57361
    Commented Oct 14, 2010 at 11:41
  • I understand trade route blocking occurs when hostile forces either block your road by putting a unit on it, either block a port by putting a naval unit close to your port city. Route blocking probably won't occur if where were a barbarian galley somewhere in the route (even the only one) between the harbours in the fog of war.
    – Adj
    Commented Oct 19, 2010 at 16:54

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