The Byzantines was an empire contuation of the roman empire but christian where most emperors were greek and the offical language was greek . A pwerful empire that last over 1000 years and was destroyed in 1204 when their capital was pillaged by the western europeans in what was meant to be a friendly stay at their city. After that it stopped being an empire and was eventually taken over by the Turks with the famous siege of Constaninoupole and its destruction on 29th May, 1453.
The Byzantines had a powerful army and controlled massive parts of europe, asia and africa for many hundreds of year.