The Magic Sanctum is basically just the barracks for training magical type units. Higher levels increase the efficiency at which you train each unit, and unlock more advanced units. These units have special abilities that have a 30% chance to trigger each battle you send them to. For a given unit's abilities please see their individual unit page. However, mage units take the longest of all troop types to train, and do not make a good farming unit in higher levels as they take a long time to replenish and march.
Max level: 40
Training speed bonus per level: 2%
Max training speed bonus: 60%