Crystals are the source of mana from which the entirity of gameplay mechanics are based upon. Mana stored in the crystal is mined by familiars after they built up a Sanctuary around it. It can be destroyed by enemy troops to cut off mana supply. It is possible for Crystals to be depleted. Although normally this is not a problem as battles don't typically last long, this fact should still be kept in mind in long battles where the player is required to hold off attackers for 30 minutes, or should the player carelessly use their mana up, they may find themselves wanting.