Sometimes “heroic” seems the wrong word for much of the world’s ancient heroic literature: the Iliad is up to its neck in blood and guts, and a lot of classical and early-medieval stories, from all over Europe, positively swim in gore. We may be liable to anachronistic sensitivity, but even so, too much of this stuff can be hard to take. Maybe it’s salutary to be reminded that most national literatures, historically speaking, start out on the human slaughterhouse floor.

The Old Irish Táin is very old: its medieval manuscripts record centuries of oral tradition. Not exactly an epic, the tale is nevertheless conceived on a grand scale and tells of the incursion into Ulster of the forces of Connacht’s Queen Mebh, in search of the prize brown bull of Cúailnge. The Ulster armies, who have been laid low by a curse, can do nothing to stop the invasion, and it is a young hero, Cú Chulainn, who alone holds the enemy at bay. An expert in industrial-scale carnage, Cú Chulainn destroys the Irish army’s fiercest and best, until the Ulstermen revive and Mebh retreats.

Reduced to these bare bones, the plot seems basic enough; but the Táin, and beyond it the figure of Cú Chulainn himself, have had potent roles to play in much more modern Irish literature. W. B. Yeats derived his evolving mythic alter ego, Cuchulain, from Lady Gregory’s Victorian version of the Ulster Cycle, thus rendering the figure barely usable for future generations. It was not until 1969, and the poet Thomas Kinsella’s translation of the Táin, that Cú Chulainn took the first breaths of his fully post-Yeatsian life. Kinsella’s achievement was to transmit the text in clear and forceful English, preserving rather than glossing over much of its strangeness and savagery. This made for a work that brought the energies of early Irish writing to bear on an increasingly dark and violent modern Ireland.

Ciaran Carson’s decision to undertake the Táin is, in the light of Kinsella, a brave one; it is also, as it turns out, entirely justified. Carson hopes that his new translation “will be taken as a tribute” to Kinsella. This is only right, for Carson, like many another Irish poet, has been indebted over the years to something in the bleak but dignified austerity of the Kinsella Táin when writing about the complex, embittered and bloody manifestations of tribal conflict altogether closer to his own time. Kinsella staked a literary claim for the Táin not as a historical curiosity but as a classic text; and one test of such status is a text’s ability to demand and sustain repeated translations over the years.

Carson brings to bear two important senses of the Táin’s potential. In the first place, he is a poet whose attunement to the Irish language has always been acute, and a grasp of the dynamics of oral storytelling has been a major force in his own writing. As well as this, Carson can approach the Táin from the north, as it were: where Kinsella’s version seemed to tremble with the foreboding of internecine strife, as something threatening and partly alien, Carson’s translation comes out of a long intimacy with the effects of conflict, and even with its untidy and conditional cessation.

Cú Chulainn is a fascinating monster. He is a young man in the Táin, but behind him there are boyhood deeds to rival those of Hercules, and in his guerrilla campaign on behalf of Ulster there are staggering feats of wanton bloodshed. When he is in the mood for some slaughter, Cú Chulainn goes into a kind of surreal spasm: “His body revolved furiously inside his skin,” turning him into “a contorted thing, unrecognisably horrible and grotesque”. Carson’s rendering of this transformation is just right: its straightforwardness makes sure the outlandish details remain terrifying: “His heart belled against his ribs like a bloodhound guldering for its food, or a lion roaring through bears.” That Ulster “guldering” outstrips Kinsella’s rather tame “baying of a watch-dog”; and the more direct Carson becomes in effects like these, the more horrifyingly vivid Cú Chulainn’s deeds become. The Táin is a saga of extreme violence, in which there is everything from grandeur and high style to black jokes and sexual earthiness. Carson’s translation does justice to all these elements.

The climax of the Táin comes when Cú Chulainn finds himself in single combat with his dearest friend, Fer Diad, and kills him after days of sustained fighting. Neither party is happy about the conflict, and each, in his own way, has been tricked into the situation; but the two heroes exchange verses in which sorrow and regret mix with pride and hostility: the whole episode has a complexity of effect which is, as Carson shows, still far from exhausted. Cú Chulainn’s lament, after killing his friend, ends starkly, with “you dead, I bursting with life. / Courage has a brutal core”. The Old Irish for this last line, “Valour is an angry combat”, is lame in literal translation, and Kinsella’s “Bravery is battle-madness” doesn’t really come to life. Carson’s line achieves something like a tragic weight, adequate as it is not only to its immediate context in the story, but to the contemporary context of this ancient account of violence and grief in Ulster. Carson’s Táin, as natural in style as it is unflinching, is a translation of power, grace and resonance.