[3] Flann's earliest datable works are from the years following the battle of Clontarf (1014), when Máel Sechnaill mac Domnaill of the Uí Néill resumed his reign as High King of Ireland (1014-1022).
[6] A number of Flann's poems appear in the Lebor Gabála Érenn—the Book of the Invasion of Ireland—and his works on the Tuatha Dé Danann were influential,[7] while a couple concern world history or themes from classical literature.
[8] The most influential was Réidig dam, a Dé, do nim, a lengthy metrical history of the world kings of Eusebian tradition which appears to be related to Bede's Chronica Maiora.
For example, Eoin MacNeill considered Flann to be the first of the synthetic historians; his supposed synthesis of biblical history and foreign world chronicles with Irish annals, myths, and genealogical records was to be much emulated by subsequent writers.
A quatrain on Flann appears in an anonymous poem on the episcopal court of Áed úa Forréid (bishop of Armagh, 1032–1056), composed between 1032 and 1042; it provides a brief but probably near-contemporary thumbnail sketch of the man.