The Meryas were a probably Finno-Ugric tribe which lived in the region of Moscow, Rostov, Kostroma, Jaroslavl and Vladimir. They may have been related to the Mari, or even more likely to the Mordvins and the Vepses between whom they lived. They were an old and important culture which is shown in the numerous archaeological finds in those areas.
They are mentioned by the 6th century Gothic scholar Jordanes as the Merens and later by the Russian chronicles.
They were assimiliated by the Slavs.
See also:
References
Uvarov, "Étude sur les peuples primitifs
de la Russie. Les mériens" (1875).