The reign of one of this polity's rulers and his allegedly demonic wife was chronicled in The Secret History by Procopius.
This polity legendarily regained the true cross after it won at the Battle of Nineveh. Earlier, it had been rocked by the Acacian Schism after reconciliation with the Miaphysites failed. In later times, the holders of its highest office employed a retinue of elite Viking warriors called the Varangian Guard. The reign of one of this polity's rulers and his allegedly demonic wife was chronicled in The Secret History by Procopius. The Isaurian and Paleologus dynasties ruled this empire. For 10 points, name this empire that came to an end when Mehmed II defeated Constantine XI Paleologus during the siege of Constantinople.
This polity legendarily regained the true cross after it won at the Battle of Nineveh.
Byzantine Empire [or Byzantium]