Today, Italy's folk music is often divided into several spheres of geographic influence, a classification system proposed by Alan Lomax in 1956[1] and often repeated since. The Celtic and Slavic influences on the group and open-voice choral works of the north contrast with the Arabic, Greek, and African influenced strident monody of the south. In central Italy these influences combine, while indigenous traditions like narrative and ballad singing remain. The music of the island of Sardinia is distinct from that of the rest of Italy, and is best known for the polyphonic chanting of the tenores.