Editing Wisrtum:The Magic of Wisrtum

Arcane magic is a powerful, yet fickle art, powered by manna that permeates the world; as it has done since the dawn of creation. The degree of manna saturation over extremely large areas is not completely uniform. Most areas are sufficiently saturated with manna to allow the sufficiently gifted to wield magic. At some points in the earth, powerful conduits of magic, called lay-lines run, producing increased manna saturation: where these lines intersect is produces even more heavily saturated manna zones. In some places, manna is strongly conducive to the casting of some spells, and not others. Perhaps the most infamous and perplexing of which, the Narmer desert region. In defiance of the understanding of even the most learned of sages, Narmer strongly favors the casting of death-magic and makes the casting of curative spells difficult at best for both mage and cleric alike. In addition, some areas are void of manna, making the casting of arcane magic a complete impossibility.  

Clerical magic, often a gift of the gods, by contrast has little to no relation to manna. Clerical magic is workable to the degree that a god has sanctified a given area, and thus has dominion over it. Most areas of the world allow clerical magic to work unimpeded, with Temples to that god being variously more favorable to the working of such magic. By contrast, an area strongly coveted by a rival god will probably be too strongly defiled to permit the working of clerical magic by the former. In such cases, the cleric cut-off from his god has two options: flee to an area less defiled by a rival god. Or, the use of some divine relics may permit some degree of connection with his god, even in such an awful place as the stronghold o a rival god.