(Θράσυλλος), a musician of Phlius. is mentioned by Plutarch (de Mus. 21, p. 1137f.), in connection with Tyrtaeus of Mantineia and Andreas of Corinth, as having purposely abstained from many of the artificial refinements which were introduced at an early period into Greek music. From the way in which he is mentioned by Plutarch, he seems to have lived in the early part of the fifth century B. C.
[P.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890