The Second Book of Swords — Fred Saberhagen

For a game the gods have given the world twelve Swords of Power, so that they might be amused as the nations go to war for possession of them. But Vulcan Swordmaker has had his little joke: the Swords can kill the gods themselves. What started out as a Divine Jest has become all too serious. Now the gods want their swords back-- but even gods must tread most carefully when faced with the Swords of Power...