We primarily understand Ammianus Marcellinus through his own accounts. Born around 330 AD in Antioch, Syria, into a respected Greek family, he likely received his initial education there. At the time, Antioch was a major Roman Empire city, celebrated for its wealth, which Ammianus took pride in. However, he viewed the diverse populace of Greeks, Jews, Syrians, and others with less favor, noting their penchant for luxury and pleasure, though he felt criticisms of them were somewhat overstated. Despite this, Greek intellectual leadership persisted, and Antioch remained a fertile ground for education, producing notable figures like Libanius and Joannes Chrysostom.

Ammianus’s career spanned the reigns of several emperors in the latter half of the fourth century, a time when the empire’s prestige declined, culminating in the catastrophic loss at Adrianople in 378, where Emperor Valens died. Early in his life, Ammianus joined the protectores domestici, an elite imperial bodyguard unit, thanks to his noble birth. By 353, he was working with Ursicinus, the East’s military commander, experiencing both triumphs and challenges, notably at Nisibis, Mesopotamia. His narratives provide a unique glimpse into Ursicinus’s character, otherwise little known.

Ammianus witnessed key events and participated in significant campaigns, including defending Nisibis against Persian forces. His adventures brought him close to danger but also showcased his dedication and resourcefulness, especially during the siege of Amida, from which he narrowly escaped.

After Ursicinus’s dismissal in 360, Ammianus’s subsequent activities are less clear, though he participated in Julian’s Persian campaign in 363. He spent considerable time in Antioch, likely immersing himself in study and preparation for his historical writings, which were primarily focused on his military years.

Ammianus eventually moved to Rome, possibly after 378, engaging with the intellectual community there and forming connections with figures like Symmachus and Praetextatus. Despite not being a Christian, Ammianus held a liberal view towards the Church and advocated for religious tolerance, often referring to a supreme divine power in his writings.

The exact date of Ammianus’s death is unknown, but references within his work suggest he was alive in 391 and possibly as late as 393. His legacy, particularly his detailed and vivid accounts of fourth-century Roman life and military campaigns, remains invaluable for understanding the period.