Chinese music is among the oldest musical traditions, dating back as far as 3000 BCE, however, it only began to be documented in detail from around 960 CE onwards. Early Chinese sources suggest applications of music in the court, military, and for folk festivals. The Zhou dynasty (1050-221 BCE) formally established court and ceremonial music. Around this time especially, music was seen as a direct expression of nature. The Chinese tonal system prioritised modes with five core tones (the pentatonic scale) and this was seen as connected with the five elements of fire, water, earth, wood, metal. The subsequent Imperial China era marked an influx of musical styles and influences being introduced through trade and religion. This was particularly prevalent during the Tang dynasty (618-907 CE) where the imperial growth led to an increase in commercial music. This period also set the stage for Chinese theatrical music, and more importantly, opera. The Ming and Qing periods popularised this musical form. Narrative-based songs, as well as Se and Guqin (both zither instruments) instrumental music became highly popular. Whilst Chinese musical tradition covers a variety of styles, there are some common features. The music is heavily melodic based on the pentatonic scale with no strict sense of chordal accompaniment. The texture is often heterophonic, meaning that one specific melody will be continuously repeated or mimicked with varying degrees of ornamentation and adaptation. Common instruments are the Dizi (a side-blown bamboo flute), the erhu (a two-stringed bowed fiddle), the yunluo (a gong chime consisting of multiple suspended gongs), and the sheng (a mouth-blown organ).