For others named Rhesus, see Rhesus.
Odysseus and Diomedes stealing Rhesus' horses, red-figure situla by the Lycurgus Painter, ca. 360 BC
Rhesus, 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.
Rhesus takes place during the Trojan War, on the night when Odysseus and Diomedes sneak into the Trojan camp. This is the same event depicted in book 10 of Homer's the Iliad.

Controversy
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.