Unicorns are a mythological equine animal very similar to the horse but with a long horn protruding from between their eyes and several other minor structural differences. They are generally held to be stronger and more spirited than horses. In several of Harry Turtledove's fantasy series, unicorns appear. In both the Darkness and The War Between the Provinces series, unicorns are domesticated animals and are used in warfare by all combatants. In Derlavai, the unicorn exists alongside the horse, while in Detina it appears to have replaced the horse altogether, though it still coexists alongside the donkey.
Unicorns co-existed with horses in the magical world that Captain Hasso Pemsel found himself in. While one element of the mythology Pemsel was aware of, namely that only virgins could ride unicorns, was untrue, it did take strong magical abilities to do so. Hence, they were the favoured mounts of wizards.
Much to Pemsel's surprise, he found his latent magical talents allowed him to master unicorns. He proved this to a group of doubtful wizards by mounting and riding one of their steeds. He also enriched his purse since they wagered he couldn't do it.
It had long been assumed that unicorns would only allow the tall, blond, blue-eyed Lenelli to ride them and would not tolerate any of the short swarthy Grenye on their backs - one of the points which the Lenelli habitually cited as "proof" of their racial superiority.
However, when the Grenye army was on its way to a decisive confrontation with the invading Lenelli, they encountered in a wood a unicorn who allowed Lord Zgomot, the Grenye ruler of Bucovin, to ride him - to the great surprise of Zgomot himself. This greatly boosted the morale of the Grenye, who saw it as a good omen towards the coming battle - and so it indeed proved.
When flying carpet transporting it broke down, a unicorn broke out of its cage and became very agitated. David Fisher, who was commuting by, wondered if they could a find a virgin anywhere in Angels City that could calm the beautiful beast. A nunnery, he thought before he passed out of sight and mind of the scene, might be their only option.
Unicorns would have been the ideal cavalry steed, if not for the fact that it created intense feelings of sexual arousal in any person who rode it who was not a virgin. Eunuchs were tried, but they weren't aggressive enough. Children were also tried, but they didn't make adequate soldiers. Women soldiers didn't work, either. The only person who was able to ride a unicorn and keep his mind on the battle was Coradin, nicknamed Honeymouth.
The animals had white fur, long flowing tails and a single horn in the center of its forehead. They strongly resembled legendary unicorns so the name was applied automatically. An immediate dispute arose among the savants in the expedition as to whether they should be classified among the horse kind or the goat kind. Since males had a single hoof on each foot and females had two, no immediate resolution could be reached.
The mage Kyosti wondered what preyed on the beasts since their numbers were significantly less than the plants which formed their food supply. One specimen was sacrificed as bait, being laid out in an outcropping with several marksmen hiding nearby. In this way, the expedition first discovered the large reptiles they named dragons.