Abstract This study examines clitic placement and the use of contracted forms in 13th-century medieval Spanish, focusing on the works of Gonzalo de Berceo. The results indicate that, although proclisis was the predominant norm, unexpected enclitic usages appear, especially in initial position and after metrical caesuras. These occurrences suggest that Spanish at the time was in a transitional stage regarding the fixation of clitic position. Metrical patterns and parallel syntactic structures also influenced clitic distribution, revealing an interaction between linguistic norms and stylistic constraints. Furthermore, the analysis identifies contracted forms affecting not only third-person pronouns but also first- and second-person forms, although their usage was not fully standardized. These findings support the view that the evolution of clitics in Spanish was a gradual process, shaped by phonological, syntactic, and discourse-related factors, with poetic composition offering a space in which grammatical rules and artistic expression coexisted and interacted.