: I hate to be rude but it's rather stupid to say a fort is
: a castle. Still, it's a fortification and I guess
: that's your point.
Going from the Warhammer Siege Glossary of Siege Terms, a Fort is "A small military fortification usually without permanent living quarters."
: City walls are not castles.
No, but they can be classed as fortresses ("A major fortification or a castle, usually protecting a city or other important settlements.")
As to why we don't see castles elsewhere, bear in mind the fact that The Province, where most of the remains of civilisation lie, are mostly plains. Let's say you're the king of the Province, and you want to fortify your realm. Three main courses of action are available to you:
1) Built city walls/fortresses around your cities. While costly, this provides the maximum protection for your people.
2) Built Citadels, which your people can then retreat to in times of danger. While less costly, this means surrendering your towns to be burned to the ground by the enemy.
3) Built independently standing forts or castles, in the hope that, by blocking the easiest routes to your populated areas and by cutting off supply lines, you may prevent the enemy from doing serious harm to you. Since there is so little obstructing terrain in the Province, building forts or castles there is frankly stupid unless they're built at the passes, since the enemy can just go around them, and still get at your populated centres.
