The Byzantine Empire or Eastern Roman Empire, known to its inhabitants as the Roman Empire, the Empire of the Romans (Greek: , Basileía tôn Rhōmaíōn), Romania ( , Rhōmanía), or Romais ( Rhōmaís), was the continuation of the Roman Empire during the Middle Ages, centered on its capital of Constantinople, and ruled by Emperors in direct succession to the Roman Emperors. The Empire preserved Roman legal traditions, but due to its Hellenization (especially in the later periods),Ahrweiler & Laiou (1998), 3
* Davies (1996), 245
* Moravcsik (1970), 11–12
* Lapidge (1998), 79
* Winnifrith–Murray (1983), 113
* Gross (1999), 45 it became known to some of its contemporaries as the Empire of the Greeks. In the Islamic world it was known primarily as lang: روم (Rûm "Rome"). The term "Byzantine Empire" postdates the Empire itself, and was popularized by historians during the 16th–19th centuries.

The Eastern Roman Empire's evolution from the ancient Roman Empire is sometimes dated from Emperor Constantine I's transfer of the capital from Nicomedia (in Anatolia) to Byzantium on the Bosphorus, which became Constantinople (alternatively "New Rome"). By the 7th century, the Empire had taken on a distinct character; reforms under Emperor Heraclius (610–641 AD) changed the nature of the Byzantine army and recognized Greek as the official language.

During its thousand-year existence the Empire remained one of the most powerful economic, cultural, and military forces in Europe, despite setbacks and territorial losses, especially during the Roman-Persian and Byzantine–Arab Wars. After the Komnenian restoration briefly re-established dominance in the 12th century, the Empire slipped into a long decline, with the Byzantine–Ottoman Wars culminating in the Fall of Constantinople and its remaining territories to the Muslim Ottoman Turks in the 15th century.

Nomenclature

The term "Byzantine Empire" is an invention of historians and was never used during the Empire's lifetime. The Empire's name in Greek was Basileia ton Rhōmaiōn ( )— "The Empire of the Romans"— a translation of the Latin name of the Roman Empire ( ); or just Rhōmania ( ). The term "Byzantine" itself comes from "Byzantium", the name that the city of Constantinople had before it became the capital of Constantine. This older name of the city would rarely be used from this point onward except in historical or poetic contexts.

The designation of the Empire as "Byzantine" began in Western Europe in 1557, when German historian Hieronymus Wolf published his work Corpus Historiæ By­zantinæ, a collection of Byzantine sources. The publication in 1648 of the Byzantine du Louvre (Corpus Scriptorum Historiæ Byzantinæ), and in 1680 of Du Cange's Historia Byzantina further popularized the use of Byzantine among French authors, such as Montesquieu. It was not until the 19th century, however, with the birth of modern Greece, that the term "Byzantine" came into general use in the Western world.