Aulus Gellius, Attic Nights 6.5
A story about the actor Polus, which is worth relating:
There was once a very famous actor in Greece, who was preeminent among his peers due to the distinctness and delight of his manner and voice. They say that his name was Polus, and he acted many of the tragedies of the great poets very seriously and with great skill. This Polus lost his most preciously cherished son to death. Once he seemed to have sufficiently worked through his grief, he returned to the pursuit of his art.
At that time in Athens, he was about to perform Sophocles’ Electra, in which he was required to carry an urn as though the bones of Orestes were inside. The argument of the play was so composed that Electra, as though she were bearing the remains of her brother, should bewail and lament his supposed death. Therefore Polus put on a mourning habit and took the urn from the tomb of his son, and as though he were grasping the bones of Orestes, he choked up not with representations and imitation, but with real grief and truly breathing lamentation. And so, though it seemed that everyone was watching a play, it was a performance of real grief.”
Historia de Polo histrione memoratu digna. Histrio in terra Graecia fuit fama celebri, qui gestus et vocis claritudine et venustate ceteris antistabat: nomen fuisse aiunt Polum, tragoedias poetarum nobilium scite atque asseverate actitavit. Is Polus unice amatum filium morte amisit. Eum luctum quoniam satis visus est eluxisse, rediit ad quaestum artis. In eo tempore Athenis Electram Sophoclis acturus gestare urnam quasi cum Oresti ossibus debebat. Ita compositum fabulae argumentum est, ut veluti fratris reliquias ferens Electra comploret commisereaturque interitum eius existimatum. Igitur Polus lugubri habitu Electrae indutus ossa atque urnam e sepulcro tulit filii et quasi Oresti amplexus opplevit omnia non simulacris neque imitamentis, sed luctu atque lamentis veris et spirantibus. Itaque cum agi fabula videretur, dolor actus est.