There are many types of spells, each with different rules about when they can be cast and who they can be cast upon: Strategic- Strategic spells can only be cast from the world map (not in tactical battles). Tactical- Tactical spells can only be cast in tactical battles. Unless otherwise specified, the duration lasts only for that battle. For example, if a unit is Hasted in tactical combat, it only gains that bonus for that battle. Universal- Universal spells can be cast either in tactical combat or from the world map. Some spells have slightly different effects depending on if they are cast in tactical combat or on the world map. For example, if an Earth Elemental is summoned in tactical combat it only lasts for that battle. For example, if an Earth Elemental is summoned on the world map then it stays with that army, but has a mana maintenance cost that must be paid each turn. Enchantment- Enchantment spells are cast on units and can be used to make your units more powerful or protect them. Most have a mana maintenance cost that must be paid each turn. City Enchantment- City enchantments affect cities much as enchantments affect units. They can boost the research for that city, help defend it, or provide a variety of other benefits. Most have a maintenance cost.