It was a time when fragments, lost poems, and early pages of unfinished manuscripts mattered. In 1938 the poet Antonio Machado, his mother, and his brother made their way from Spain to France to escape Franco’s advancing fascist forces. When Machado died in February 1939 in Collioure, his brother found in his pocket the first line of his last poem: “Those blue days, this childhood sun.”

In 1942, when the poet Miguel Hernández died in prison, where he had languished after the Spanish Civil War, he left a body of work that was later published as Cancionero y romancero de ausencias (Songs and Ballads of Absence, 1958) . Some of his best-known poems were written on scraps of paper.

The most famous among these poets was Federico García Lorca, who was murdered by fascist soldiers near Granada in the south of Spain in August 1936. Lorca left much unpublished and half-finished work, both poems and plays.…