Italian Folk music has a deep and complex history. National unification came quite late to the Italian peninsula, so its many hundreds of separate cultures remained un-homogenised until quite recently compared to many other European countries. Moreover, Italian Folk reflects Italy's geographic position at the south of Europe and in the centre of the Mediterranean Sea – Arabic, African, Celtic, Persian, and Slavic influences are readily apparent in the musical styles of the Italian regions. Italy's rough geography and the historic dominance of small city states has allowed quite diverse musical styles to coexist in close proximity. Today, Italy's Folk music is often divided into several spheres of geographic influence. The Celtic and Slavic influences on the group and open-voice choral works of the north contrast with 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.