The first version of Ainulindalë (known as The Music of the Ainur) was intended to be part of Tolkien's The Book of Lost Tales, written in the 1910s and 1920s and published by Christopher Tolkien in the first two volumes of The History of Middle-earth. In a letter to Christopher Bretherton, dated 16 July 1964, Tolkien wrote the first version of Ainulindalë between November 1918 and the spring of 1920, while he was working on the Oxford English Dictionary.