Castanets, also known as clackers or palillos, are a percussion instrument (idiophone), used in Spanish, Kalo, Moorish, Ottoman, Italian, Sephardic, Swiss, and Portuguese music. In ancient Greece and ancient Rome there was a similar instrument called crotalum.The instrument consists of a pair of concave shells joined on one edge by a string. They are held in the hand and used to produce clicks for rhythmic accents or a ripping or rattling sound consisting of a rapid series of clicks. They are traditionally made of hardwood (chestnut; Spanish: castaño), although fibreglass is becoming increasingly popular.