Ivan III the Great vs Theodosius I

Ivan III married Sophia (Zoe) Palaiologina, niece of the last Byzantine emperor. This marriage allowed Ivan to claim succession to the Byzantine Empire, adopt the double-headed eagle as a symbol, and promote Moscow as the Third Rome.

Ivan III conquered the Novgorod Republic after a series of campaigns. He abolished the veche (assembly) and removed the veche bell, incorporating Novgorod's vast territories into the Grand Principality of Moscow.

Ivan III faced the Mongol army of Khan Akhmat across the Ugra River. After weeks of stalemate, the Mongols withdrew without battle. This event ended 240 years of Mongol suzerainty over Russia.

Ivan III promulgated a new legal code, the Sudebnik, which standardized laws across the Russian lands. It restricted peasant mobility by limiting the time for transfer between landowners, a step toward serfdom.

Ivan III launched a war against Lithuania, capturing the cities of Bryansk, Dorogobuzh, and Putivl. The war ended with the Truce of 1503, which ceded significant territories to Moscow.

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.