The Byzantine Empire, or Eastern Roman Empire, was the continuation of the Roman Empire in the medieval period, although over the centuries, it gradually became primarily Greek. The capital was Constantinople, now known as Istanbul. For a thousand years, the Empire was a powerful force, despite military setbacks and territorial losses, but entered into a lengthy decline after the twelfth century, culminating in the Fall of Constantinople to the Ottoman Turks in 1453.The imperial flag featured a double-headed eagle to symbolize the empire’s interests in both Europe and Asia. (via Dark Roasted Blend: Flags of Forgotten Countries)