Cleonides (Κλεονείδης ὁ μουσικός) was a Greek music theorist of the Roman imperial period, traditionally dated to the 2nd century CE, though some scholarship proposes a later date in the 3rd or 4th century [1]. No biographical details of his life survive beyond the name transmitted in his work's manuscripts [2].

His sole extant work is the Eisagōgē harmonikē (Εἰσαγωγὴ ἁρμονική), or Introduction to Harmonics, a concise and systematic treatise summarizing the harmonic theory of Aristoxenus [1][2].

Cleonides's significance rests entirely on this treatise, which became a primary and highly influential textbook for understanding Aristoxenian music theory. Its clarity ensured the transmission of core concepts—notes, intervals, scales, genera, and modulation—throughout the Byzantine and medieval Latin traditions [1].

Sources 1. Stanford Encyclopedia of Philosophy (Stanford University): https://plato.stanford.edu/entries/aristoxenus/#Cle 2. Perseus Digital Library (Tufts University): http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.01.0239:chapter=1