The Seikilos epitaph is the oldest known complete composition of music in existence, a Hellenistic Ionic song with complete notation likely inscribed in the first century AD. And its notation have allowed modern music scholars to play the song in the modern day.
Although there are certainly older musical texts and fragments, the very brief Seikilos epitaph is a complete song, found engraved on a tombstone near Aidin, Turkey, along with the inscription, "I am a tombstone, an image. Seikilos placed me here as an everlasting sign of deathless remembrance."
The song also has lyrics, translated from the Ancient Greek:
While you live, shine
have no grief at all
life exists only for a short while
and time demands its toll.
The History Blog points to a recent BBC article that details ancient Greek musical notation. It also notes that David Creese, a Lecturer in Classics at Newcastle University, constructed a zither-like instrument called a "canon," with eight strings and movable bridges, which he has used to play the song on the Seikilos epitaph, utilizing the scale-ratios provided by the mathematician Ptolemy in the second century AD. Below is one of Creese's versions of the song, including the lyrics:
Michael Levy, an ancient music researcher who frequently performs on his own version of an ancient lyre, has performed his own version of the song, sans singing:
Photo from the National Museum of Denmark.