Rhesus (Ρήσος, Rēsos), possibly 350 BC, is transmitted among the plays of Euripides, and was indeed believed to be genuinely Euripidean in the Hellenistic, Imperial, and Byzantine periods. As early as the 17th century, however, the play's authenticity was cast into doubt, first by Joseph Scaliger and subsequently by others. Its authenticity was defended in a book-length study by William Ritchie (1964), but his conclusions were forcefully opposed by Eduard Fraenkel in a review that remains a classic of philological acumen to this day.
In the middle of the night Trojan guards on the lookout for suspicious enemy activity sight bright fires in the Greek camp. They promptly inform Hector, who almost issues a general call to arms before Aeneas makes him see how ill-advised this would be. Their best bet, Aeneas argues, would be to send someone to spy on the Greek camp and see what the enemy is up to. Dolon volunteers to spy on the Greeks in exchange for Achilles's horses when the war is won. Hector accepts the deal and sends him out. Dolon leaves wearing the skin of a wolf, and plans on deceiving the Greeks by walking on all fours. Rhesus, the neighboring king of Thrace, arrives to assist the Trojans soon after Dolon sets out. Hector berates him for coming so many years late, but decides better late than never. Rhesus says he intended on coming in the beginning, but was sidetracked defending his own land from an attack by Scythians.
Meanwhile, on their way into the Trojan encampment, Odysseus and Diomedes run into Dolon and kill him. When they reach the encampment with the intention of killing Hector, Athena guides them to Rhesus' sleeping quarters instead, pointing out that they are not destined to kill Hector. Diomedes slays Rhesus and others while Odysseus takes his prized horses before making their escape. Rumors spread from Rhesus' men that it was an inside job, and that Hector was responsible. Hector arrives to cast blame on the sentinels for, due to the sly tactics, the guilty party could only be Odysseus. The mother of Rhesus, one of the nine muses, then arrives and lays blame on all those responsible: Odysseus, Diomedes, and Athena.
This short play is most notable in comparison with the Iliad. The part with Dolon is pushed to the background, and much more is revealed about Rhesus and the reactions to his murder by the Trojans.
According to Gilbert Murray in his introduction to Rhesus, passages from "Euripides'" Rhesus were quoted by early Alexandrian writers. However, there was some doubt shed on the authenticity of the work by ancient introductions. The first to fully dispute that Rhesus was a play by Euripides was L. C. Valckenaer in his Phoenissae (1755) and Diatribe in Euripidis deperditorum dramatum reliquias (1767). (Ancient History Sourcebook) Most scholars have agreed with Valckenaer, but there are some who still believe the play to be by Euripides. Stylistic differences are one of the main arguments of the controversy. Murray, in dissent of the popular opinion, claims the differences in style could be attributed to a younger, less developed Euripides. Or the differences could be attributed to it being a reproduction by Euripides' son or other contemporary playwright.