Monsters occupy a hallowed place in Sword & Sorcery for a lot of reasons. One, they make for cool artwork. Many an S&S novel has gone to press with a giant spider, or a monster squid, or a dragon on the cover. Second, they add a supernatural element when there is no actual wizard in the story. If the tale is just pirates killing each other, then that might be a Sword & Sorcery tale, but add a lost city with a demonic guardian, and you’re home. Third, they create dramatic, powerful enemies for the protagonist to do battle with, solving one of the common problems of writing S&S.
Because S&S heroes and heroines are often depicted as tremendously bad ass. They are barbarians who come from a harsh background, they have been through battles and wars, they have faced down armies and bandits and kings and evil wizards, so after a while it starts to be hard to come up with anyone for them to fight who could present a challenge. After all, barbarian warriors are not Batman – they don’t take their enemies prisoner. They kill them. That means recurring villains are hard to do, and you are left trying to establish a whole new threat every time.
And here is where monsters come in to save the day. Monsters, after all, are not bound by the rules of mortal flesh. They can be huge, armored death machines, dripping with scales and claws and slime. They can be immune, or mostly immune, to the weapons the characters wield. They can regenerate or come back to life unless they are killed properly. There can be a lot of them, or just one of them. They can provide as much threat as you need.
At the same time as they add tension and danger, they can add atmosphere and scope to a story. Many of the creatures used in the classic S&S tales are, essentially, prehistoric. Giant snakes and lizards are common, as well as huge insects or overgrown spiders. These fit with the themes of Lovecraftian horror, evoking a world in which man is but prey, and setting current action against a backdrop of deep time that lends itself to an atmosphere of doom and human insignificance. Prehistoric animals like dinosaurs also add a layer of plausibility to a story, as these were creatures that really existed, even if they never walked the earth with human beings.
Some of them, however, really did, and stories often include Pleistocene megafauna like mammoths or saber-toothed tigers. This adds a certain aura of stone-aged savagery to a world, and suggests a place that is more primitive and primordial than our own planet. Even simply juxtaposing things like mastodons with a more civilized fantasy world creates a more exotic, interesting mood.
Scope is another consideration, and adds to the reasons why monsters are awesome in a story. Monsters are, after all, larger than life. A battle against a band of raiders may be gritty and brutal, but it will never have the grandiose quality of a heroic stand against a giant or a demon. Battle against a more than human foe elevates a character beyond heroic and into the realms of legend. Some of our oldest myths are about heroes who did mortal battle with terrible monsters: the chimera, the minotaur, jotuns and dragons and sea monsters.
Because monsters symbolize things, fighting and killing a monster elevates the whole story to another level. Killing other humans may speak of man’s inhumanity, or whatever is going on, but killing a monster is striking at the deepest evils in our imaginations, killing off the terrible outside apparitions that stand in for our terrors of things too big for us to face, things that we can’t actually kill. You can’t kill fear, but you can kill the monster that causes fear. You can’t fight winter, but you can kill the frost giants that stand for it. Monsters have always stood in for the forces too large and too powerful to be embodied in human form.
Plus, they look kick ass on a book cover.