The Cairn on the Headland is a short story by American writer Robert E. Howard, with elements of fantasy and horror. As often in Howard stories, there is a link to the Cthulhu Mythos, in this case mixed also with elements of both Norse Mythology and Catholic Christianity.
It has a rather convoluted history, being in effect an adaptation of Howard's earlier story Spears of Clontarf, a historical adventure story by Howard focusing on the Battle of Clontarf (1014) and featuring Turlogh Dubh O'Brien or Black Turlogh, a fictional 11th Century Irishman created by Howard. Howard later rewrote "Spears" as "The Grey God Passes", which was very similar to Spears of Clontarf, but with added fantasy elements. Howard failed to sell the story in either version during his lifetime.
"The Cairn on the Headland" (Howard's third version of Spears of Clontarf) was a horror story set in the present, and succeeded in getting published in Strange Tales (January, 1933). It was later reprinted in August Derleth's Skull-Face and Others, as well as in Lancer Books' paperback collection Wolfshead.
(The Grey God Passes was posthumously published in a 1962 Arkham House hardcover Dark Minds, Dark Heart, while Spears of Clontarf was finally published in an eponymous 1978 chapbook).
Plot summary
James O'Brien is an Irish-American researcher who specializes in the history of Medieval Ireland - a subject which he is highly well-informed on and has a passionate feeling of partisanship towards. He speaks Gaelic fluently, can read ancient Irish manuscripts or inscriptions in their original state. and is thoroughly familiar with such works as The Book of Leinster, the Great Book of Lecan, and the Annals of the Four Masters.
O'Brien's promising academic career, and his life's work, is threatened by an insidious blackmailer named Ortali. Ortali is now in possession of evidence which could implicate O'Brien in a murder he didn't commit. With this threat hanging over his head, O'Brien must give Ortali much of his salary and the money he got from various academic awards. Ortali enjoys taunting O'Brien and humiliating him.
While visiting Dublin, O'Brien and Ortali discover an ancient cairn on a hillside. The area is shunned by the local citizens, and therefore remains nearly unchanged since the Middle Ages - though the bustle and bright lights of modern Dublin are just around the corner. It's known that the cairn was erected in the aftermath of the 1014 Battle of Clontarf, when Brian Boru liberated his kingdom from an army of Vikings. However, O'brien isn't sure if this structure was erected by the victorious Irish or by the defeated Norse, and who is buried underneath.
Ortali decides on coming back around midnight and dismantle the cairn, in the hope of finding treasure under it. O'Brien strongly objects to Ortali's decision, both because it's a historic landmark and he feels a premonition about what lays beneath it. Ortali ignores O'Brien's advice and his view towards superstition. When O'Brien mentions how local citizens believe holly should never be brought near the cairn, Ortali simply laughs and says he will wear a bundle of holly on his lapel when he returns.
The two also argue about the Battle of Clontarf - O'Brien regarding King Brian Boru as not only having freed Ireland from centuries of Viking oppression, but also having saved all of humanity from the occult worship of the Norse deity Odin, whose followers abandoned their ancestral beliefs and eventually embraced the White Christ. Ortali laughs and scoffs about that, too. The two part in great anger, separately walking back to their hotel. Soon, O'Brien picks up a jagged stone and conceives the idea of killing Ortali with it - even though he would then be charged with a murder of which he would be truly guilty.
Later, O'Brien encounters a mysterious woman, who wears archaic clothing and speaks an ancient version of Gaelic. She introduces herself as Meve MacDonnal and gives O'Brien a golden crucifix, decorated with tiny jewels, of an extremely archaic and unmistakably Celtic workmanship. After a moment, he recognizes it as a legendary relic, the Cross of Saint Brandon, which was considered lost centuries ago.