The Byzantine Empire, which existed independently from 395 to 1204 A.D. and from 1261 to 1453 A.D., was known as the Eastern Roman Empire (or Romania) during the Middle Ages. It was one of the most powerful economic, cultural, and military forces in Europe, despite some setbacks and territorial losses due to wars. Its existence is owed to a series of actions which started with the division of Rome's Empire into eastern and western halves in 285 and ended with its complete separation in 395. During its long history it was ruled by a series of emperors from its capital city of Constantinople (also referred to as the New Rome). Its peak population is estimated to have been 26 million in 565 A.D.
The empire's economy was, for several centuries, one of the most advanced in the world. This was mainly due to Constantinople's strategic location (at a point where Europe meets Asia) and its role as one of the primary ports for the famous Silk Road (route that facilitated trade between China, India, Egypt and Europe) which made it a wealthy economic hub.
Although his reign began before its full independence (306 A.D.), Constantine the Great (Constantine I) is considered the first ruler of the Byzantine Empire. He made Byzantium (renamed Constantinople after his death) his capital and under his reign brought to the forefront the major characteristics of the Byzantine state.
Emperor Constantine's influence on the history and beliefs of Christianity is significant. Up to the time of his rule the Roman empire had initiated, since the time of Nero, several waves of harassment and persecution against those who believed in the Bible. The first wave of Rome's wrath, which started in 67 A.D., is believed to have taken the lives of the apostles Peter and Paul. The second wave, begun under Domitian in 81 A.D., exiled the apostle John to the island of Patmos and martyred the evangelist Timothy (Apostle Paul's traveling companion and closest friend). Seven other periods of persecution followed which killed countless numbers of believers. The last of ten attacks against believers, which ran from 284 to 305 A.D., was Rome's most vicious. Constantine, in his 313 A.D. Edict of Milan, ended 230+ years of violence by legalizing Christianity. His action eventually led to Christianity being made the official state religion of the empire in 380 A.D.
Around 1071, after years of dominance, the empire lost most of its heartland (Asia Minor) to the Seljuk Turks. It received a mortal blow in 1204 A.D. by the Fourth Crusade, when it was dissolved and divided into competing Greek and Latin realms. Despite the re-establishment of the Empire in 1261 A.D., under the Palaiologan emperors, successive civil wars in the 14th century further sapped the Empire's strength. The complete disintegration of the Empire culminated with the Fall of Constantinople and its remaining territories to the Muslim Ottoman Turks in the 15th century.