On April 1, 527, he became sole Emperor, and he reigned till 565. Constantinople under Justinian became again the centre of Christian Europe. But before his power was fully established it was threatened by the gravest of the great insurrections with which the populace showed its independence and its fickle levity. The sedition arose in the Circus, and it was long the fashion to believe that Constantinople was ruled entirely under the sway of the factions of the Hippodrome. A more critical investigation has shown that the demes (δῆμοι) or parties were organised bodies intimately connected with the court and the municipality. The demes had two parts, military under democrats, and civil, or political, under demarchs. The heads of each faction were officers of the court and the army, and the demes were fully organised for military purposes. Not only were they, as we have seen, intrusted with the building of the wall, but they provided, under the Emperor Maurice, troops for the guarding of the long walls; and Justinian himself, at the end of his reign, used them in a similar way. It was to the demes, one writer seems to show, that Justin owed his throne. But while their military and political importance is now fully recognised, we are still without an explanation of how they became connected with the parties and colours of the Circus. However that may be, we find in the reign of Justinian two large Circus parties, the Blues and the Greens, with whom were merged as sub-divisions the Reds and the Whites, who organised the races and had so much liberty allowed them by the laws, that they were able to defy emperors and set public order at defiance. But the madness of their riot was not without a method. To the demes or factions were allowed privileges which seemed the last relics of the ancient freedom of the Greek cities. "In the sixth century," says Professor Bury, "the outbreaks of the demes represent a last struggle for municipal independence, on which it is the policy of imperial absolutism to encroach. The power of the demarchs had to give way to the control of the præfects of the city." [Illustration: THE IMPERIAL QUARTER]