[3] Though often an outsider figure, for instance in the role of intervener or arbitrator, Cú Roí appears in a great number of medieval Irish texts, including Forfess Fer Fálgae, Amra Con Roi, Brinna Ferchertne, Aided Chon Roi (in several recensions), Fled Bricrenn, Mesca Ulad and Táin Bó Cúailnge.
This story is related to the "beheading game" motif appearing in many later works in Arthurian literature - most famously the 14th-century English poem Sir Gawain and the Green Knight, although closer correspondences are to be found in Diu Crône and La Mule sans frein, both of which feature a revolving fortress like Cu Roi's.
The resulting encounter (comlond) between the two warriors is a spectacular stone-throwing contest, described from the perspective of the Connacht troops, who witness many stones flying in opposite directions from the east and west (Cotal and Ard Róich) and colliding right above their heads.
The shower of falling rubble forces them to use their shields for protection, until on their request, Cú Roí and Munremar agree to discontinue the fight and return home.
However, on finding Cú Chulainn weak from the injuries which Ferdiad had recently inflicted on him, he refused to carry out his original plan.
Instead he faces the giant warrior poet Amairgin, who in a trance is hurling stones at the Connacht army in Tailtiu, with devastating effects.
The episode in the Book of Leinster (Recension II), called Imthúsa Chon Ruí meic Dáire (header) or Oislige Amargin (text),[9] offers by and large the same story, but adds more explicit detail, notably on the point of Cú Roí's sense of honour in his encounters with Cú Chulainn and Amairgin.
Medb insisted "[b]y the truth of your [Cú Roí's] valour" ([a]r fír do gascid fritt) that he should abandon the competition, obstructive as it proved to be to the progress of the expedition.
Cú Roí, however, was determined to persist "till the day of doom" (co brunni brátha) unless Amairgin agreed to stop.
However Ferchertne, Cú Roí's poet, enraged at the betrayal of his lord, grabbed Bláthnat and leaped off a cliff, killing her and himself.
First, it occurs in the corrupt form Cubert m. Daere in the Middle Welsh tale Culhwch ac Olwen, along with the names of other characters of the Ulster Cycle – Conchobor, Fergus, Conall Cernach and Lóegaire Búadach.
[12] Second, an elegy (marwnat) for Corroi/Corroy m[ab] Dayry is preserved in the Book of Taliesin, which mentions his contention with "Cocholyn", or Cú Chulainn.