If you haven’t read much history, you may be aware that the Roman Empire fell in 476 AD. If you have read a bit more history, you’ll be fully aware that the Western Roman Empire fell then … the rest of it lasted nearly another thousand years. Richard Blake, who has a very readable series of novels set in the “blind spot” of history between the collapse of the West and the revival of the Eastern Empire, offers a quick thumbnail sketch of the historical background to his fiction:
In 395 AD, following a century of experiment, the Roman Empire was divided into Eastern and Western administrative zones, with joint Emperors in Rome and in Constantinople. The purpose was to let each Emperor deal with the pressure on his own critical frontiers – the barbarians along the Rhine and Danube frontiers in the West, and the Persians along the Euphrates and desert frontiers in the East.
In theory, each Emperor was equal. In practice, the Eastern Emperor, ruling from Constantinople, was soon the senior partner. During the next two hundred years, becoming increasingly Greek in language in culture, the Eastern Empire flourished, and Constantinople became one of the largest and most opulent cities in the world.
The Western Empire went into immediate and rapid decline. In 406 AD, barbarians crossed the Rhine in large numbers, and broke into Italy. In 410 AD, they sacked Rome. By then, the Western Capital had been moved to Ravenna, a city in North Eastern Italy, impregnable behind marshes, and within easier reach of the frontiers – and within easier reach of Constantinople.
During the next seventy years, the Barbarians took France and Spain and North Africa from the Empire. Britain remained in the Empire, but its people were told to look to their own defence. In 476 AD, the last Western Emperor was deposed. By 500 AD, the whole of the Western Empire had been replaced by a patchwork of barbarian kingdoms.
After 527 AD, the Emperor Justinian began to reach out from Constantinople to reconquer the lost Western provinces. He recovered North Africa and Italy and part of Spain. However, the effort was exhausting. After his death in 568, the Empire lost much of Italy to the Lombard barbarians, and Rome itself fell under papal domination. Slavic and Avar barbarians crossed the Danube and conquered and burned all the way to Athens and the walls of Constantinople. After 602, the Persians began a war of destruction against the Empire. Though they ultimately lost, they did briefly take Egypt and Syria.