Leo III the Isaurian vs Sviatoslav I

Leo III successfully defended Constantinople from a massive Arab siege by the Umayyad Caliphate. The siege lasted from 717 to 718. Leo used Greek fire and a harsh winter to defeat the Arab fleet and army, saving the Byzantine Empire from conquest and halting Arab expansion into Europe.

Leo III reorganized the Byzantine military and administrative system, strengthening the theme system. He created new themes and improved the defense of the empire. These reforms increased the empire's military effectiveness and administrative efficiency.

Leo III issued the Ecloga, a legal code that revised and simplified Roman law. The code was written in Greek and emphasized Christian principles, including greater protection for the poor and women. It influenced later Byzantine and Slavic legal systems.

Leo III issued an edict banning the veneration of icons, initiating the first period of Byzantine Iconoclasm. He ordered the destruction of religious images and persecuted iconodules. This policy caused deep religious divisions within the empire and strained relations with the Papacy.

Leo III led the Byzantine army to a decisive victory over the Umayyad Arabs at the Battle of Akroinon. The Byzantine forces destroyed the Arab army, ending the Arab threat to Anatolia for decades. This victory consolidated Byzantine control over Asia Minor.

Sviatoslav led a campaign against the Khazar Khaganate, capturing the fortress of Sarkel and sacking the capital, Atil. This destroyed the Khazar state, ending its dominance over the steppes and opening the Volga trade route to Rus control.

Sviatoslav invaded the First Bulgarian Empire at the request of the Byzantine Emperor. He defeated the Bulgarian army, occupied much of the country, and established his capital at Pereyaslavets on the Danube, threatening Byzantium.

After a three-month siege by Byzantine forces under Emperor John I Tzimiskes, Sviatoslav's army was defeated at Dorostolon. He was forced to surrender, renounce claims to Bulgaria, and withdraw from the Balkans.

Returning to Kiev, Sviatoslav was ambushed and killed by the Pechenegs at the Dnieper Rapids. The Pecheneg chief Kurya made a drinking cup from Sviatoslav's skull. His death ended his expansionist campaigns.