read the manual and be mindful of where you post :
http://www4.imperiaonline.org/forums/int/index.php?topic=26.0Fortresses hitpoints and garrisons:
(these are the basic numbers, Fortification and Military architecture is increasing them along with the terrain factors)
Hit points Garrison
Level 1 48 000 100 (Stone tower)
Level 2 96 000 200 (Walled stone tower)
Level 3 192 000 400 (Citadel)
Level 4 576 000 800 (Fortress)
Level 5 1 152 000 1600 (Fortress with Citadel)
Level 6 4 608 000 3200 (Fortress complex)
Level 7 9 216 000 6400 (Legendary Fortress)
Level 8 18 432 000 12800