Music was an important part of cultural and social life in Ancient Greece: mixed-gender choruses performed for entertainment, celebration and spiritual ceremonies; musicians and singers had a prominent role in ancient Greek theater.[9] In the 9th century, the Arab scholar al-Farabi wrote a book on music titled Kitab al-Musiqi al-Kabir ("Great Book of Music"). He played and invented a variety of musical instruments and devised the Arab tone system of pitch organisation, which is still used in Arabic music.