Unicorn.   Equus uniceros.  Capra uniceros.
 

There are actually two varieties of unicorn, the horse (E. uniceros) and the goat (C. uniceros), but this story is of the white horse with the magical horn.
 

"...After the great battle between the Tuatha De Danann and the fierce Firbolgs,  the Goddess Herself appeared among the remnants of Her victorious people.  She wandered among the mortals, giving blessings to those who lay dying and the gift of Her healing touch to those who could be saved.  During the course of Her wandering, She happened upon a great white  horse.  The poor beast stood on splayed legs, sides heaving mightily, and nose almost touching the ground.  Blessing him with speech, she asked gently, 'Are you wounded?'   'Nae, Mistress, I am not wounded.'  'Then why do you stand there in such low spirit?' She asked the beast.  The horse answered in a weary voice saying, 'Goddess Danu, I am called a war-horse.  It is true that I use my hooves and teeth during battle to help my master, but they are weak weapons.  I have allowed my master to be killed.  I am shamed.'  The Goddess took pity on the war-horse and taking his head gently between Her hands, She placed a kiss upon his forehead.  To the amazement of the beast and those mortals around him, an ivory horn sprung from the spot upon which the kiss had been placed.  Immediately, the great horse sank to his knees and thanked Danu for Her gift.  'I will call you Unicorn, She told the animal.  Now go and learn to use your new weapon.'  Unicorn turned and trotted gaily from the scene of the battle, swinging his head, brandishing the gleaming horn.  He happened upon some young warriors who had not been in the battle and they agreed to teach him swordplay.  To the horror of the great Unicorn, and the mortal souls around him, he miscalculated his thrust at the first young warrior and gored the youth through the heart.  With a scream of shame and anguish, the beast galloped from the scene and was never seen no more."
 

This is the only account I have found of this incident, but it is taken from a book which has been well documented.  Knowing no reason, why such a tale would be invented and included in a history, I set out to research this beast.  These are my findings:
 

Unicorn wandered alone through the wilds of Eire for a full year, mourning the loss of his master and and the murder of the young, unnamed warrior.  After a time the Goddess, sensing his misery, visited Her magical stable and chose the best filly of Her stock.  As with Unicorn, She blessed Uniceras with the gift of speech, and placed the kiss upon her forehead.  She sent Uniceras to find Unicorn and keep him company.
 

Unicorn was gladdened by the presence of the filly and soon forgot his misery.  But being aware of the dangers of the weapons upon their foreheads, he exacted a promise from Uniceras that she would never again seek the company of humans.
 

There are many tales of scant glimpses of unicorns throughout history.  These unicorns are the descendants of Unicorn and Uniceras.  Most of the tales were brought to England by travelers and the unicorn became a mythical legend along with the tales of the De Danann faerie folk.  Note that the English, rather than the Irish, were the people who made the unicorn famous.  They searched for the unicorn relentlessly because they believed the horn to be magical with healing powers.  They haunted the beasts and slaughtered them unmercifully.  Because of Uniceras' promise and this great slaughter, the unicorn has become the most secretive animal on Earth.  Sorrowfully, the horn is only useful to a living unicorn and its only magic is in its first creation.
 

The male and female unicorns are usually of the same size.  The overall appearance is that of a dainty horse, Arabic in proportion and size.  The mane and tail are extremely long and silken and tufts of this mane hair grow from the chin and the hock.
 

The foals are born almost helpless and cannot stand or walk for several days.  It is believed that this is reverse "survival of the fittest" in that the foals which are adventurous and strong are more easily captured by humans.  They are born with a mottled dun coat which helps to hide them in the forests and mountains they call home.  The coat gradually lightens to become the brilliant white of the adult.  Immature unicorns stay with their sire and dam for a period of about 7 - 8 years, learning to survive in a world which names them legend.
 

The horn begins to sprout at about four years and takes about three years to develop into a powerful weapon.  In olden times, the horn was used to fight off bears, lions, and wolves.  Being that those animals are now extinct in Ireland, the unicorn has no need of battle skills except when threatened by humans.
 

Unicorns are not herd animals like their cousins the horses, but live in family groups of three.  The sires teach the young ones about Uniceras' promise and the stealth they need to stay hidden.  The mares provide the care and grooming.  When two family groups meet, they may travel together for a day or two, but generally they tend to stay separate.  A small family group is harder to spot than a herd of six.
 

The animals have been known to graze with domestic horses, keeping their heads low to hide their horns and chin hair.  These days it is much harder for them to be inconspicuous because farmers know their own animals and do not welcome strays.
 

When the young unicorn reaches maturity, it leaves its parents and begins a solitary life which lasts about ten years.  Very little is known of the reason for this sojourn, but it rumored to be a sort of homage to the Goddess Danu, a time in which the young animal learns of its own inner strengths.  It is during this period that most unicorns are seen by humans.  Many stories have been told of captured unicorns promising to lead its captor to gold if it is released.  But the freed unicorn is a swift and intelligent animal and can quickly "disappear" from sight.
 

After the solitude, the now mature animal seeks out a mate.  The gestation period lasts from 30 to 32 months.  When a mare finally gives birth, she is generally about 20 years old.  The mated pair raises only one or two foals during their lives which is why the beasts are so rare.
 

After the last offspring leaves the parents, the two generally live out the remainder of their lives without the company of others.  When elderly unicorns feel that Death is near, they travel to the northern sea.  Once there, they embed their horns in rock to snap them off, then leap into the sea further protecting the secret of their existence.

The most recent capture of a unicorn happened in the early 19th century.  A young English lad visiting the mountains somehow managed to come between a young animal and the mouth of the gully in which it had bedded.  The youth quickly lassoed the beast in the manner of American cowboys and was amazed when the animal spoke to him in the ancient Gaelic tongue.  Not understanding the language, the young man called out for his companions.  While his attention was diverted, the beast used its horn to cut through the rope, leaped over the lad, dodged the companions and escaped.  No verifiable sighting of a unicorn has been reported since.

I hope this essay satisfies your curiosity.  I have given my word that I would never divulge my source.  The unicorn wishes to be left to itself to worship the Goddess and raise its young.  Sadly, there are few of them left in Ireland with little room to roam.  With the mistrust and ill feelings between unicorn and human kind, they have had no opportunity to cross the seas to other places.
 

Remember, if you ever see a unicorn, delight in the sight, but leave him to his peace.
 

Domestic horse.  E. caballus
Domestic goat.  C. hircus

The essay is mine - the art is not.  I took it from the web.  Links are provided for those I could remember.