Proto-Slavic and contrasted only after alveolars and labials. After palatals only occurred, and after velars only occurred. With the development of phonemic palatalized alveolars and labials in Old East Slavic, and no longer contrasted in any environment, and were reinterpreted as allophones of each other, becoming a single phoneme . Note that this reinterpretation entailed no change in the pronunciation and no mergers. Subsequently, (sometime between the twelfth and fourteenth centuries), the allophone of before velar consonants changed from to with subsequent palatalization of the velars. Hence, for example, Old Russian became modern . Conversely, the soft consonants were hardened, causing the allophone of to change from to .