All castles in Heroes 3.

Not always. Skeletons are the first level, the main striking force of Necromancers. Archers from the Castle are the second level, they shoot twice. Elven Archers are the third level, they shoot twice. Orc Archers are the third level, Wolf Riders are the second level - they hit twice and have high speed. Harpy Witches are the second level, they have speed and attack, and then return. Lizard Archers are the second level, the only archers of the swamp; Snakes are the third level, with their speed, they are quite effective. Cerberuses are the third level, they have an unreturned attack. And so on. So, Warriors of levels 1-3 are useful not only for defense.