Gratian vs Yazdegerd II

Valentinian I elevated his eight-year-old son Gratian to the rank of Augustus (co-emperor) at Amiens. This was intended to secure the succession and stabilize the Western Roman Empire. Gratian was placed under the tutelage of experienced officials.

Gratian's generals led Roman forces to a decisive victory over the Alamanni at Argentovaria (modern Colmar, France). The battle crushed the Alamanni threat to Gaul. Gratian personally led the pursuit of the defeated tribes, earning military prestige.

Under the influence of Bishop Ambrose of Milan, Gratian refused to wear the robes of the Pontifex Maximus, the traditional title of the Roman emperor as chief priest of the pagan state religion. He also removed the Altar of Victory from the Roman Senate, symbolizing the end of official paganism.

The Roman general Magnus Maximus was proclaimed emperor by his troops in Britain. He invaded Gaul and confronted Gratian near Paris. Gratian's army deserted him, and he fled to Lugdunum (Lyon), where he was captured and executed by Maximus's forces.

Yazdegerd II launched a military campaign against the Byzantine Empire, attacking Roman territories in Mesopotamia. The war ended inconclusively after a few years, with both sides agreeing to a truce that maintained the status quo.

Yazdegerd II issued an edict demanding that the Christian population of Armenia convert to Zoroastrianism. This sparked widespread resistance and rebellion among the Armenian nobility and clergy, leading to the Battle of Avarayr in 451 AD.

Yazdegerd II's forces defeated the Armenian rebel army led by Vartan Mamikonian at the Battle of Avarayr. Although the Sasanians won militarily, the battle became a symbol of Armenian resistance, and Yazdegerd later granted religious concessions.