E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Damon and Pythias.
Inseparable friends. They were two Syracusian youths. Damon, being condemned to death by Dionysius the tyrant, obtained leave to go home to arrange his affairs
if Pythias became his security. Damon being delayed, Pythias was led to execution, but his friend arrived in time to save him. Dionysius was so struck with this honourable friendship that he pardoned both of them.