I think there's no one to disagree that fort are pretty useless! I personnally NEVER use them unless on a narrow passage with hill on edge of my cultural border which never really happen! My idea on how to improve is that they could be add up one on the other! Reaching up in level as you work on it... for example lv.1 Fortification (actual fort +25% def) lv.2 Fort (35% def + healing like a city) lv.3 Castle (50% + heal + resist to cultural border as city does) lv.4 Stronghold (need stone +75% + heal + resist cul - 25% if on hills) lv.5 Some famous stronghold (need stone and hill +100% + heal + res. cul.) Plus we need to make it AWFULLY long to get to Lv.5 so people cant really build them everywhere! or even limit them or exaust 1 Stone Ressources once lv.5 built! the - 25% on lv4 is too avoid over powering it too soon and make it more like a step toward lv5.