The
chelys (, ), was a
stringed musical instrument, the common
lyre of the ancient Greeks, which had a convex back of
tortoiseshell or of wood shaped like the shell. The word
chelys was used in allusion to the oldest lyre of the Greeks, which was said to have been invented by
Hermes. According to the
Homeric Hymn to Hermes (475) he was attracted by sounds of music while walking on the banks of the Nile, and found they proceeded from the shell of a tortoise across which were stretched tendons which the wind had set in vibration.