Music theory has existed since the advent of writing in ancient times. The earliest known practitioners include primarily Greek and some Chinese scholars. A few Indian sages such as Bharata Muni (Natya Shastra) are also credited with important treatises. Though much is lost, substantial treatises on ancient Greek music theory survive, including those by Aristoxenus, Nicomachus, Ptolemy and Porphyry. The influential Yue Jing Classic of Music from China is lost, though a few Ancient Chinese theorists from the Han dynasty and later have surviving contributions, such as Jing Fang and Xun Xu.