The heraldic unicorn is a result of increasing secular interest in unicorns in Europe. While the bestiaries described the creature as very small and similar to a kid, later depictions favored the horse-like unicorn of Pliny. An important inspiration was Ludovico di Varthema, who saw two unicorns in the temple in Mecca, which had the body of a horse, the head of a hind and slender legs with cloven hooves, like those of a goat.
Pliny said the unicorn cannot be caught alive, but scholars of the Renaissance could not accept this assertion without a supporting explanation. And so it was answered, as Guillim tells us, that such is the greatness of his mind that he more readily chooses death over being caught alive. In this, he is similar to a valiant man, as they both so far contemn death, that they prefer to die than be compelled to any base servitude or bondage.
While people of the Middle Ages ascribed beneficial properties to all parts of the unicorn's body, especially the heart, later the virtues were concentrated in the horn. And so in the Greek bestiaries we read that in the evening all animals gather at the watering place, but find that a serpent has left its venom floating on the surface. Seeing or smelling the venom, they do not dare to drink, but instead wait for the unicorn. When at last he approaches, he dips his horn in the water, neutralizing poison and making it safe for all again. Therefore, the unicorn represents both strength and courage, as well as virtuous dispositions and the ability to do good. For to have the strength of the body without the virtues of the mind is but the property of an ox. But where both concur, that may truly be called manliness.
The lion is the unicorn's enemy and rival in the contest over who should be the king of beast. Great is the lion's strength, but even he is afraid of his opponent's sharp horn. Therefore, he resorts to a trick: he stands in front of a tree and taunts the unicorn, who then charges at him in full gallop, trying to gore him. A moment before impact, the lion slips aside, and lets the unicorn pierce the tree and be unable to remove the horn. Then the lion kills his foe.
Two unicorns have long been supporters of the Royal coat of arms of the Kingdom of Scotland and became one of its symbols. Carrying a unicorn on the escutcheon is often taken to signify service done to or in that country. In 1603 James VI of Scotland acceded to the throne of England and combined the heraldry of those two kingdoms; for supporters, he took the lion from the English arms and made him stand next to his Scottish unicorn. Since that time, unicorn lore became an interest of British scholars. The act of uniting the former enemies was often taken as symbolic to the reconciliation between the frequently warring nations of England and Scotland.