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), While walking on the banks of the Nile, Hermes was attracted by sounds of music, which he found came from tendons stretched across the shell of a tortoise which the wind had set in vibration. Also see lyre and kithara (cithara).