This story is told in first-person narrative and includes his journey to find a home as he travels through Wales, Brittany, England and Ireland.

Educated by a hermit, Galapas, who teaches him to use his psychic powers as well as his earthly gifts, Merlin eventually finds his way to the court of Ambrosius Aurelianus in Brittany.

He is captured by Vortigern who is attempting to build a fortress at Dinas Emrys – but each night the newly built walls collapse.

Merlin helps Uther to enter Tintagel Castle by stealth, knowing the tryst will lead to the birth of King Arthur.

[2][3] The hill is considered by the locals to be a home or haunt of a deity named Myrddin, a god of air and heights, so its cave is imbued with magical properties.

"[4] The Guardian spoke of Stewart's own considerations as well as that of her publishers: "The Crystal Cave (1970), the first of a fictional trilogy about Merlin, arose from her fascination with Roman-British history.

The Hollow Hills (1973) and The Last Enchantment (1979) completed the trilogy, earning Stewart favourable comparisons with another leading Arthurian, TH White.

"[5] Kirkus Reviews said with a touch of disdain, "With its mythic mists and galloping legends, fifth century Britain is fair game and Miss Stewart takes to whole cloth with a couturier's skill.

"[6] The novel was adapted into a television series by the BBC in the 1990s, retitled Merlin of the Crystal Cave, and starred Robert Powell as Ambrosius.