[1] Its motifs became popular in medieval and later Arthuriana, notably the introduction of the sword in the stone, the redefinition of the Grail, and turning the previously peripheral Merlin into a key character in the legend of King Arthur.

Along with the poems attributed to Robert de Boron – the romance Joseph d'Arimathie, which survives only in prose, and Perceval, perhaps completely lost – Merlin forms a trilogy centered around the story of the Holy Grail.

The Grail, brought from the Middle East to Britain by followers of Joseph of Arimathea, is eventually recovered by Arthur's knight Perceval, as foretold in one of the prophecies in Merlin.

An alternative theory postulated by Linda Gowans goes against the widely accepted conventional scholarship in deeming the prose text to be the original version of Merlin.

[9] The first part introduces the character of Blaise [fr], a cleric and clerk who is pictured as writing down Merlin's deeds, explaining how they came to be known and preserved.

It continues with the story of the usurper king Vortiger (Vortigern) and his tower, featuring the seven-year-old Merlin with amazing prophetic powers.

The poem seems to have ended with the later "sword in the stone" story, in which Arthur proves he is to become Britain's high king by a divine destiny.

This has been the first instance of this motif to appear in Arthurian literature; it has become iconic after being repeated almost exactly in Thomas Malory's popular Le Morte d'Arthur.

[2] The following is the complete text of the mid-15th-century English translation (medieval English versions replaced the Anglo-Saxon enemies of Britain with the Saracens, the Danes, or just unidentified heathens), with modern conventions for punctuation and capitalization, of the prose version (sans the sequels): Merlin is regarded as having been followed by the third part in Robert's Grail cycle, Perceval, however this poem is either entirely lost or perhaps was never even really written.