Whenever a civilization finishes a Trade Route to a certain city for the first time (that is, the route runs its allotted number of turns), it creates a Trading Post in the City Center district of the destination city. Your merchants use the connections they've established and buy some property there, where they create a permanent support station for future commercial activities. This post has the following effects:
- It extends the range of Trade Routes which pass through the city by 15 tiles, which is also the base trade route range. If a Trade Route reaches a city with a Trading Post, it may then continue up to fifteen additional tiles to reach another city. If that city also has a Trading Post, the route may extend a further fifteen tiles, and so on.
- Each Trading Post also adds +1 Gold to every route originating in the trader civilization which passes through this city.
Trading Posts can exist in both foreign and domestic cities, and multiple civilizations can establish Trading Posts in the same city. Civilizations cannot make use of Trading Posts established by other civilizations.
Trading Posts that are in foreign cities are vital for extending trade range far beyond a civilization's borders. Domestic Trading Posts can allow a particularly productive core city to supply a developing border city directly, and can also enable wealthy core cities to trade directly with foreign cities.
All Roads Lead to Rome, the Roman civilization ability, gives a further +1 Gold to Roman Trade Routes which pass through a Roman city with a Trading Post. It also provides a free Trading Post to every city Rome founds or captures, as well as a road if the city is within trade range of the Capital. This ensures all Roman Trade Routes, especially those originating in the Capital, have long ranges and a wide choice of destination cities.
Örtöö, the Mongolian civilization ability, instantly creates a Trading Post in any city to which the Mongolians send a Trade Route and provides them with an extra level of Diplomatic Visibility with any civilization that has a Mongolian Trading Post in at least one of its cities.