Auras
Copyright 2013 M&M Flebotte and S. Koziel
Aura can be hidden, or altered so while the ability to sense an aura other then what a mage is attuned to is useful and certainly helps in manipulating mana during spell casting it is not necessary that a mage be able to see all forms of mana to cast.
If a mage can not sense the specific tone or tempo of mana they usually can not cast spells that use that specific form of mana. Very rare cases have been documented of mages being able to "cast blind" in which they can not fully sense the specific type of mana they are working with, though this is most often accomplished by accessing spells or items that
give a person a limited sense or convert a mages actions into something that can manipulate the mana they can not sense. Usually this involves a great deal of ceremony or multiple casters.
Natural reservoirs of mana can form and if they are large enough they will cause fortresses to form out of the surrounding environment. Once these mana structures form a specific mage will be drawn to the structure. A mage drawn to a fortress becomes it guardian and they are meant to keep the magic in the area unpolluted. In ancient times magical technologies were developed that exploited the fortresses, and their "closeness" to the dimensions their magic is most like to produce a permanent gate to the other dimension.
