The early part of the work is largely mythical, depicting the history of Ireland as a succession of invasions and settlements, and derives primarily from medieval writings such as the Lebor Gabála Érenn, the Dindsenchas, royal genealogies and stories of heroic kings.
[3] The work was extremely popular, surviving in a large number of manuscripts,[5] and its prose style became the standard followed by generations of Irish-language writers.
[6] It has been said that it had "an influence on Irish language and literature as significant as Shakespeare's role in relation to English" .
[7] However, it was received critically from the start by some with Sir Richard Cox (1650–1733), a Protestant lawyer of English descent, describing it in the 1680s as "an ill-digested heap of very silly fictions".
[3] Modern scholars consider in the context of the antiquarian tendency of Renaissance humanism, with Keating expounding on ancient Irish sources, whose authority he defends, to provide "an origin-legend for Counter-Reformation Catholic Ireland.