Constantine founds the new capital of the Roman Empire on the existing site of the ancient Greek city Byzantium: Byzantium was renamed Constantinople and it would become the capital of the Byzantine Empire.
The Roman Empire divides in half, with the Eastern Roman Empire based in Constantinople and the Western Roman Empire based in Rome/Ravenna.
The Western Empire Falls: The Eastern Empire survives and now is labelled as the Byzantine Empire.
Justinian's reign begins. He reconquers parts of the fallen Western Empire (Africa and Italy, Spain). He codifies the Previous Roman Laws into one document. Constantinople is the most glorious city in europe, with 500,000 inhabitants. The Hagia Sofia is constructed. Justinian is the last emperor to use the title "Caesar".
Lombards invade Italy, eventually taking Northern Italy from the Byzantines.
Heraclius becomes emperor. Temporary possession of Mesopotamia. The theme system is installed. The Empire's language changes to Greek. Eventual Lost of Syria, Palestine, and Egypt to Muslims.
Muslims attack Constantinople.
Emperor Leo III bans the use of Icons.
Charlemagne, king of the Franks, is crowned "Emperor of the Romans" by Pope Leo III in Rome. For the first time in 300 years, there is an emperor of the "East" and an emperor of the "West".
The use of Icons is restored.
Prince Igor of Kiev attacks Bithynia and later attacks Constantinople: The Byzantines destroys the Russian fleet.
Basil II becomes Emperor.
Basil II reconquers Syria from the Muslims.
Basil II reconquers Greece from Bulgars.
Basil II destroys the Bulgar army, earning the epithet Bulgaroktonos ("Bulgar Slayer").
The Great Schism: The Latin Roman Church and the Greek Orthodox Church excommunicate each other.
Loss of southern Italy to the Normans.
Defeat at Manzikert to the Seljuk Turks. Permanent loss of most of Asia Minor.
Loss of Syria to Muslims.
Byzantines defeated in Thrace.
Alexius appeals to Urban II at Council of Piacenza for help against the Turks. The First Crusade is proclaimed at Council of Clermont.
Crusaders arrive at Constantinople. The Crusaders are successful, but eventually withdraw from cooperation with the Byzantines.
Byzantine Army defeated by the Sultanate of Rum at Myriokephalon. Hopes of regaining Asia Minor are lost.
Fourth Crusade is assembled at Venice.
Fourth Crusade captures Constantinople. The Latin Empire of Constantinople is formed as well as many Byzantine successor states. The capture of Constantinople in 1204 was a blow from which the Byzantines never fully recovered.
The successor state of Nicaea recaptures Constantinople and restores the Byzantine Empire.
Fall of Constantinople to the Ottomans. End of the Byzantine Empire.