Damon and Pythias, two Pythagoreans of Syracuse of the days of Dionysius I., celebrated for their friendship; upon the latter having been condemned to death, and having got leave to go home to arrange his affairs beforehand, the former pledged his life for his return, when just as, according to his promise, he presented himself at the place of execution, Pythias turned up and prepared to put his head on the block; this behaviour struck the tyrant with such admiration, that he not only extended pardon to the offender, but took them both into his friendship.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Damocles * Dampier, William