Proto-Balto-Slavic is a reconstructed proto-language descending from Proto-Indo-European (PIE). From this proto-language the later Balto-Slavic languages are thought to have developed, composed of sub-branches Baltic and Slavic, and including modern Latvian, Lithuanian, Polish, Russian and Serbo-Croatian among others. Like most proto-languages, it is not attested by any surviving texts but has been reconstructed using the comparative method.