The music of Greece is as diverse and celebrated as its history. Greek music separates into two parts: Greek traditional music and Byzantine music, with more eastern sounds. These compositions have existed for millennia: they originated in the Byzantine period and Greek antiquity; there is a continuous development which appears in the language, the rhythm, the structure and the melody. Music is a significant aspect of Hellenic culture, both within Greece and in the diaspora. Greek musical history extends far back into ancient Greece, since music was a major part of ancient Greek theater. Later influences from the Roman Empire, Eastern Europe and the Byzantine Empire changed the form and style of Greek music. Greek folk traditions are said to derive from the music played by ancient Greeks. There are said to be two musical movements in Greek folk music: Acritic songs and Klephtic songs. Akritic music comes from the 9th century akrites, or border guards of the Byzantine Empire. Following the end of the Byzantine period, klephtic music arose before the Greek Revolution, developed among the kleftes, warriors who fought against the Ottoman Empire. Klephtic music is monophonic and uses no harmonic accompaniment.