Proto-Slavic (from Balto-Slavic and Proto-Indo-European long *ē) developed into Old Russian , distinct from (the outcome of Proto-Slavic from Balto-Slavic and Proto-Indo-European short *e). They apparently remained distinct until the 18th century, although the timeline of the merger has been debated. The sound denoted may have been a higher sound than , possibly high-mid vs. low-mid . They still remain distinct in some Russian dialects, as well as in Ukrainian, where Proto-Slavic developed into respectively. The letter remained in use until 1918; its removal caused by far the greatest of all Russian spelling controversies.