The Book of the Spells of Merlin was a compendium of Celtic magic. During the Inquisition, the last known copy of the book was burned in 1384.

In August 1932, Wolfgang S. Staubig was touring Dubrovnik and found a copy of the book in an antique bookstore. Reading the book, Staubig found a section on the appearance of the Holy Grail as chalice of pewter with Aramaic inscriptions. The text by "Merlin" also offered an incantation to conjure up an image of the grail, but the copyists poorly translated the runes into Latin. Staubig received offers of help in restoring the runes from O'Lochlainn and René Belloq. Knowing that his colleague, Henry Jones, Sr. would be interested in the Grail information, Staubig wrote a letter to Jones with the pertinent information in September.

Jones noted in his journal that it was ironic that a copy of the book would turn up in Dubrovnik, when Jones had failed to find any trace of the Grail in Yugoslavia.