They are said to be the most powerful rulers who ever lived—a checkered mix of the wise, the brutal, and the unhinged. For more than five centuries they presided over a multi-ethnic empire that was nearly always at war, if not with neighbors then with rebellious factions within the empire itself. The full scope of their powers was not systematized in constitutional law, a fact that tempted many of them to overreach disastrously; and the lack of clear rules of succession meant that most of them died violently.