This paper discusses a phenomenon of Latin phonology, word-initial extrasyllabic s, a subcase of what is traditionally called s impurum. Extrasyllabic s behaves unlike other consonants in syllabification, especially at morpheme boundaries, where resyllabification takes place. The odd behaviour of initial extrasyllabic s in poetry is explained not on the basis of clashing metrical conventions but on the basis of principles inherent in the phonological system of Latin.