Gaius' Grimoire

Gaius's grimoire is a book of magical knowledge kept secretly by the sorcerer and physician Gaius, and given to his apprentice Merlin. (The Dragon's Call)

It is unclear how much of the contents of the book were discovered or developed by Gaius and how much was inherited from other sources. The book contains a spell capable of bringing inanimate objects to life, which Merlin mastered on a granite statue of a dog before performing on the magical shield of Knight Valiant. (Valiant).

The book also includes instructions for curing magical diseases, which Merlin used to heal Gwen's father when he was infected by a plague that struck Camelot. The book was nearly discovered by Prince Arthur Pendragon during a kingdomwide search for evidence of sorcerery when Gaius informed Uther that the plague's origin was magical in nature. Merlin later used the book to determine how to defeat the Afanc that had caused the plague. (The Mark of Nimueh)