[Saulot]

You should reread the quote. It said "or forts to be tied to terrains and nations."

In Dom2 you pick the fort when making a pretender. You get one fort.

In Dom3 your forts are picked for you. Each nation has up to 6 different forts that it can construct, depending on the terrain of a province in the game that you want to build on.

For example;
Sauromatia has Ramparts as a default fort (terrain with no special qualities), Fortification in a Farmland, Hillfort in mountain, Swamp Fort in swamp, and Forest Ramparts in a Forest province.

Each nation has differing selections, some superior, some inferior, but it all adds a layer of strategy and decision making as to where to build forts.