According to later tradition, Cormac the son of Art the son of Conn was king of Ireland c. 227-66 CE. This particular text (written in Middle Gaelic, thus suggesting a date of composition between the 10th and 12th centuries) was preserved in the early 16th century Egerton manuscript.
The following is a revised translation by Michael Newton based on the edition in Kuno Meyer, “Stories and Songs from Irish Manuscripts.” Otia Merseiana 2 (1900-1).
Five men of Ulster brought Ciarnat, the daughter of a Pictish king, as a captive (from a raid) across the great ocean. Cormac the grandson of Conn heard about that and sent for her by his command and she was taken to his house. She was the most beautiful and fair woman in the world in her time. She was Cormac’s mistress and he loved her immensely.
But Cormac’s wife Ethne Ollamda the daugher of Cathair the Great heard that she [Ciarnat] was with him and she said that he could not have both of them. Ciarnat was forced into Ethne’s custody and she forced her to do unfree manual labour, which was this: she had to grind nine bushels of cereal crop every day. Then Cormac (came to her) and they slept together secretly and she became pregnant so that she could no longer do the grinding.
Cormac took pity on her and brought a carpenter from across the ocean and a mill was made to liberate Ciarnat. This was the reason for the file’s [“poet’s”] verses:
“Ciarnat, the slave of good Cormac, her quern fed many hundreds,
She had to grind nine bushels every day, it was not the work of a slacker;
The noble king came upon her as she was alone in her house
So that he made her pregnant, secretly; after that she could not do much grinding
The grandson of Conn took pity on her, he brought a carpenter across the great waves:
The first (water)mill of Cormac son of Art was (made) as aid for Ciarnat.”