Julian the Apostate was a Roman emperor in the fourth century, when Christianity was already well established by the emperor Constantine. However, Julian wanted to bring history back to the pagan times. His reign was short and unexpected; it was characterized by distinctive religious reforms and the Persian campaign. He was not a historically important ruler. Many Christian writers wrote about him, mostly portraying him negatively. Nonetheless, he was a model of an ideal ruler for the pagan historian Ammianus Marcellinus, who focused on Julian in his historiographical work Res gestae, written as a continuation to Tacitus, and presented him as a ruler chosen by the gods. Despite admiration Ammianus was also critical of some of Julian's policies. Nevertheless, he also tended to intentionally diminish the meaning of religious and other matters that might damage Julian's reputation. Furthermore, Ammianus compared Julian to many famous personalities from Greek and Roman history and portrayed the previous emperor Constantius and Julian's brother Gallus in a distinctively negative way with the intention to increase Julian's importance. Despite being favoured by the gods, Julian rejected all bad omens regarding the Persian campaign, which led to his death. Ammianus parallels Julian's death with the death of Socrates and presents him as a philosopher-king. Indeed, an image corresponding to Julian's own idea of perfect ruler.