What poetic structure was used in traditional Spanish romances?

Traditional Spanish romances (folk ballads) are characterized by a specific poetic structure that has remained consistent since their early development. The form is octosyllabic, meaning each line typically consists of eight syllables.1

A defining feature of this structure is the use of assonance—the repetition of stressed vowel sounds—rather than full rhyme. In the romance form, this assonance occurs in the alternate lines throughout the poem, maintaining a single vowel sound pattern across the entire composition. This rhythmic and melodic structure allowed these ballads to serve as a vital medium for popular narrative verse, linking medieval heroic traditions to modern Spanish literature.123