Guardians of the Lost by Tracy Hickman

For two centuries the portion of the great Sovereign Stone belonging to the humans of Loerem was lost from sight and memory. But there are those who dare never forget ...

A magical relic has been miraculously recovered -- and the battle for the future of Loerem begins. It is a nightmare conflict that will ensnare dwarf, human, elf, and orken beings, as the immortal dark lord Dagnarus launches terrible war from the blackest depths of the Void. And now heros must emerge from the most unlikely corners of the world to deny Dagnarus the awesome power of the Stone -- or suffer the hideous damnation of his hellish reign.