Ardashir I vs Theodosius I

Ardashir I defeated the Parthian king Artabanus IV at the Battle of Hormozdgan. This victory ended Parthian rule and allowed Ardashir to establish the Sassanid Empire, which would dominate Persia for four centuries.

Following his victory at Hormozdgan, Ardashir I systematically conquered the remaining Parthian territories, including Media, Armenia, and Mesopotamia. He established a centralized administration and a Zoroastrian state church.

After his victory, Ardashir I was crowned 'Shahanshah' (King of Kings) at Ctesiphon. He claimed descent from the Achaemenid dynasty, legitimizing his rule and reviving Persian imperial traditions.

Theodosius I issued the Edict of Thessalonica, declaring Nicene Christianity the official state religion of the Roman Empire. All other forms of Christianity were deemed heretical, and pagan practices were increasingly suppressed.

Theodosius I ordered a massacre of thousands of citizens in Thessalonica in retaliation for the murder of a Roman general. The massacre led to his excommunication by Bishop Ambrose of Milan, and he later performed public penance.

Theodosius I issued a series of laws banning pagan worship, closing temples, and prohibiting sacrifices. The Olympic Games were abolished, and the Serapeum in Alexandria was destroyed. These actions accelerated the decline of paganism in the empire.

Theodosius I defeated the usurper Eugenius and his general Arbogast at the Battle of the Frigidus (modern River Vipava). The victory reunited the Roman Empire under a single ruler for the last time before its permanent division.

Upon his death, Theodosius I divided the Roman Empire between his two sons: Arcadius received the Eastern Empire and Honorius the Western Empire. This division became permanent, leading to the separate histories of the Byzantine and Western Roman Empires.