Secondary skills in Heroes 3.

Fortress - Defense + Ballistics
Stronghold - Attack + Ballistics.

By the way, both the Stronghold and the Fortress significantly reduce losses and increase effectiveness in terms of defense and attack, respectively. For example, Tazar with experience in attack or Kreg Heg with experience as a Weaponsmith look much better!! And even a mage won't have that many advantages over a Stronghold with a tactic that has the first turn and casts mass haste.