 Nonetheless, a universal characteristic of classical music written since the late 13th century is the invariable appliance of a standardized system of precise mensural notation (which evolved into modern bar notation after 1600) for all compositions and their accurate performance.Another is the creation and development of complex pieces of solo instrumental works (e.g., the fugue).The first symphonies were produced during the Classical period; beginning in the mid 18th century, the symphony ensemble and the compositions became prominent features of Classical-period music.