Browse fantasy art for a few hours it will become undeniable that most dragons are depicted with horns. Even in fan art for characters who are never mentioned to have horns, include horns as if it's just taken for granted that all dragons have them.

Which then leads to the question of why. Why do dragons have horns? Their closest natural relatives, creatures like snakes and reptiles, only have small horns, if any. They are not often associated with predators, but are generally a trait of herbivores who live on the defensive, like goats, elk, and oxen.

Considering how commonly authors give their dragons hollow bones or hydrogen air sacks or some other method to reduce their weight and make flight more believable, isn't it a bit counterproductive to give them a pair or two of large, dense, and heavy horns to put more strain on their wings and long necks. Especially since I can't think of many occasions where a dragon's horns led to their survival.

In what uses I can think of for them, they are merely decorative, announcing that this dragon with many / large horns is a mature male. Except female dragons often have horns too, sometimes smaller or fewer, but sometimes identical. So perhaps they are a display of maturity across both sexes.

In a more practical sense, perhaps they're intended as a barricade to keep claws or teeth away from their eyes or head, except they often go straight back and leave the head mostly exposed. This may offer some purpose, but enough to justify the weight?

Perhaps they're intended to protect the base of their skull, where they can not reach. But again, minimal coverage, but some is better than none. Spines could extend that protection while adding even more weight. Allowing a smaller dragon to curl up like a porcupine when confronted by a larger one.

Perhaps they are a method to dislodge an attacking dragon from their back, or simply offering them some upward weapon against larger foes while holding their ground against something larger or stronger.

Ramming seems like the obvious answer, since that is the general intention of horned creatures, but with their massive necks, I feel like ramming would be as or more dangerous for the dragon than their target unless only shoving them.

Perhaps the intent is to pierce when a dragon rams a target, rather than bruise or break bones. But the often downward slope of horns would make this difficult.

Intimidation is certainly an option, but when you're already one of the largest creatures alive and can breathe fire, are another few feet of horn really going to make a difference?

Or are horns are purely cosmetic with no purpose beyond perhaps mating plumage or a remainder of the western dragon's semi-satanic origins?

Or are horns there simply to make a dragon's head more intriguing to the human eye when compared to a plain, unadorned head? Falling entirely under the rule of cool, where the more cool a concept is, the more we should be willing to suspend our disbelief to accommodate it's existence, and thus invalidating this essay.