Book 25 of Ammianus Marcellinus' Res Gestae is the final part of the trilogy (books 23-25) on the emperor Julian's Persian expedition. Covering a period of eight months, from June 17, 363 to February 17, 364, it contains a series of momentous events: the death of Julian on June 26, the surprising appointment of the unexperienced Jovian as his successor, the dramatic and difficult return of the Roman army, the painful surrender of Roman territory around the upper course of the Tigris to the Persian king Sapor, and finally Jovian's sudden death. The contrast between Julian, who for all his shortcomings was a true leader of men, and Jovian, who lacked this stature and who failed to defend the integrity of the Roman Empire, gives the book the character of a diptych.