Rituals are spells which have an effect on the world map, and take an entire month (game turn) to cast. Thus, mages which are to cast a ritual have to be given that order as part of the turn. If a ritual requires gems, the mage may only use gems from a laboratory and rituals can only be cast in provinces with labs (assuming the national pool has enough gems of the required type). The gems will be withdrawn from the national inventory automatically.

Some rituals affect the entire province that they are cast in. Some of these (but not all) last longer than one turn. These are termed local enchantments. An example of such a spell is Dome of Air. Once the Dome of Air is cast, it persists in that province until dispelled. The spell is dispelled if the caster dies. Local enchantments are also dispelled if the province they affect is conquered by an enemy. The exception to that is that local enchantment powered by Blood magic will persist even if the province is conquered. They must be dispelled instead.

Rituals can be automated to be recast each month by the same mage using the [Shift]+[m] shortcut when selected and in a laboratory province. The mage will cast the spell as long as he has enough gems.

If you try to cast a spell and it doesn’t get cast, the most likely problem is that you don’t have enough gems of the correct type