Written documents exist that describe the musical culture of the Rus'. The most popular kind of instruments in medieval Russia were thought to have been string instruments, such as the gusli or gudok. Archeologists have uncovered examples of these instruments in the Novgorod region dating as early as 11th century. (Novgorod republic had deep traditions in music; its most popular folk hero and the chief character of several epics was Sadko, a gusli player). Other instruments in common use include flutes (svirel), and percussive instruments such as the treshchotka and the buben. The most popular form of music, however was singing. Bylinas (epic ballads) about folk heroes such as Sadko, Ilya Muromets, and others were often sung, sometimes to instrumental accompaniment. The texts of some of these epics have been recorded.