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Hammerwood: Greek Music and the Greek Gods
This site features an explanation of Greek music in ancient Greek society. Of note is the description of Pythagoras' work which was responsible for establishing much of the theory behind our music.
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Ancient Greek Music
This site contains 24 audio links to ancient Greek music and inscriptions as well as a link to types of Homeric (Greek) singing.
Other
Homeric Singing: An Approach to the Original Performance
A short, but intersting site that explains the theory as to how the ancient Greeks may have performed their music.