New Constantinople was a city-state on Riverworld, founded and ruled by Alexios Komnenos as basileus and his brother, Isaac, as kaisar, and located along a stretch of the River. An Eastern Orthodox state, New Constantinople was populated primarily by Rhomaioi or Hellenized citizens of the empire historians came to call the Byzantine Empire. There was also a minority of Egyptian peasants from the time of Ptolemy III, who had accepted Christianity, and became in some ways more loyal than Alexios's fellow Rhomaioi.
New Constantinople was bordered by red-skin pagans up-river who only wanted to be left alone. Down-river was the Muslim city-state of Bornu, ruled by Sultan Musa ar-Rahman. As Alexios was far more worried about Bornu, he left the pagans alone.
As time passed, it soon became clear that New Constantinople and Bornu would be at war.