 In Europe the expression of a Universal Monarchy as actual total "imperium" can be seen in the Roman Empire, and as the predominate ‘sole sovereign’ state during its Byzantine period, where the Emperor by virtue of being the head of Christendom claimed a sovereignty over all other kings even though in practice this could not be enforced.The Byzantine conception went through two phases, initially as expounded by Eusebius that just as there was one God so there could only be one Emperor, which developed in the 10th century into the conception of the Emperor as the "paterfamilias" of a family of kings who were the other rulers in the world.Such concepts were a feature of the Ottoman Empire successor state, particularly when military rule was augmented by the Caliphate.