Theme (Byzantine district)
The themes or thémata were the main military and administrative divisions of the middle Byzantine Empire. They were established in the mid-7th century in the aftermath of the Slavic migrations to Southeastern Europe and Muslim conquests of parts of Byzantine territory, and replaced the earlier provincial system established by Diocletian and Constantine the Great. In their origin, the first themes were created from the areas of encampment of the field armies of the East Roman army, and their names corresponded to the military units that had existed in those areas. The theme system reached its apogee in the 9th and 10th centuries, as older themes were split up and the conquest of territory resulted in the creation of new ones. The original theme system underwent significant changes in the 11th and 12th centuries, but the term remained in use as a provincial and financial circumscription until the very end of the Empire.
Ruins at Sergiopolis
The Byzantine Empire, also referred to as the Eastern Roman Empire, was the continuation of the Roman Empire centered in Constantinople during Late Antiquity and the Middle Ages. The eastern half of the Empire survived the conditions that caused the fall of the West in the 5th century AD, and continued to exist until the fall of Constantinople to the Ottoman Empire in 1453. During most of its existence, the empire remained the most powerful economic, cultural, and military force in the Mediterranean world. The term "Byzantine Empire" was only coined following the empire's demise; its citizens referred to the polity as the "Roman Empire" and to themselves as "Romans". Due to the imperial seat's move from Rome to Byzantium, the adoption of state Christianity, and the predominance of Greek instead of Latin, modern historians continue to make a distinction between the earlier Roman Empire and the later Byzantine Empire.
Gold solidus of Leo III (left), and his son and heir, Constantine V (right)
Constantinople was the largest and wealthiest city in Europe throughout late antiquity and most of the Middle Ages until the Fourth Crusade in 1204.
The seizure of Edessa (1031) by the Byzantines under George Maniakes and the counterattack by the Seljuk Turks
Alexios I, founder of the Komnenos dynasty