Spells and Rituals
The magic in Dominions 3 is split in two different kinds of magic: The combat spells that are cast during tactical battle and the rituals that are cast during the strategic planning & processing phase of the game.
Combat spells
There are a great number of different combat spells from different schools and paths of magic and not all of them do direct damage to unit, even if there is a great number of damage spells. There are spells that summon additional creatures into the battle, spells that provide help to allies or the caster (known as buffs) and spells that weaken the enemy.
Combat spells use fatigue and in case of the strongest spells magic gems. All spells have a fatigue cost, and if mage reaches 100 fatigue he will faint. If fatigue goes over 200 the mage will start taking damage and eventually die. Magic gems can be used to cure fatigue and carrying a gem of a magic path will count as +1 to that path for all purposes. But a mage cannot gain new paths by carrying gems of a different school and only one gem will count.
Having more skill in a path of magic makes spells from that path significantly less burdensome to cast and in some cases it can also make the spell vastly more powerful and harder to resist. Good examples of spells that scale well with power are Blade Wind, Orb Lightning and Nether Darts.
Ritual spells
Ritual spells are spells that are cast on the strategic planning phase and they use magic gems for fuel. Rituals range from summoning creatures to you side to causing damage to enemy troops or provinces. All ritual spells take one turn to cast, be it a lowly ritual of Summon Cave Drake or the powerful global enchament of Astral Corruption.
Carrying gems has no effect from rituals and the gems used for ritual spells are drawn directly from the gem pool. Occasionaly the skill of a mage in certain path has an effect of the ritual. A highly skilled Death mage can summon much more Ghosts with the aproriate spell than a mage who barely meets the requirements.