The Tain, the Tuatha de Danann and Christian Monastic Recording

Old Irish literature's preservation of pre-Christian Irish mythology, including the Tuatha De Danann and their eventual retreat underground to become the sidhe, fairy or otherworldly beings of later Irish folklore, occurred entirely through Christian monastic scribes, meaning surviving Old Irish mythological texts represent a Christianized reworking and euhemerization of earlier oral pagan tradition rather than an unmediated pagan source, a source-critical situation similar to that facing Old Norse mythology preserved through Snorri Sturluson's Christian-era Prose Edda.

The Book of Invasions, Lebor Gabala Erenn, compiled in Old and Middle Irish, presents a pseudo-historical account of successive legendary peoples settling Ireland, including the Tuatha De Danann, framed within a broader biblical chronological scheme that Christian compilers used to reconcile native Irish legendary history with scriptural world history. Ogham, an early medieval Irish alphabet consisting of notches carved along a central line, was used to write Old Irish, chiefly on stone memorial inscriptions, and though its precise origins and full range of uses remain debated among scholars, some later medieval sources associate it with druidic or magical significance beyond simple memorial inscription.